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Network Working Group J. Schoenwaelder Request for Comments: 5343 Jacobs University Bremen Updates: 3411 September 2008 Category: Standards Track

Simple Network Management Protocol (SNMP) Context EngineID Discovery

Status of This Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Abstract

 The Simple Network Management Protocol (SNMP) version three (SNMPv3)
 requires that an application know the identifier (snmpEngineID) of
 the remote SNMP protocol engine in order to retrieve or manipulate
 objects maintained on the remote SNMP entity.
 This document introduces a well-known localEngineID and a discovery
 mechanism that can be used to learn the snmpEngineID of a remote SNMP
 protocol engine.  The proposed mechanism is independent of the
 features provided by SNMP security models and may also be used by
 other protocol interfaces providing access to managed objects.
 This document updates RFC 3411.

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
 2.  Background  . . . . . . . . . . . . . . . . . . . . . . . . . . 2
 3.  Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.1.  Local EngineID  . . . . . . . . . . . . . . . . . . . . . . 4
   3.2.  EngineID Discovery  . . . . . . . . . . . . . . . . . . . . 4
 4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
 5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
 6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 7
 7.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
   7.1.  Normative References  . . . . . . . . . . . . . . . . . . . 7
   7.2.  Informative References  . . . . . . . . . . . . . . . . . . 7

Schoenwaelder Standards Track [Page 1] RFC 5343 SNMP Context EngineID Discovery September 2008

1. Introduction

 To retrieve or manipulate management information using the third
 version of the Simple Network Management Protocol (SNMPv3) [RFC3410],
 it is necessary to know the identifier of the remote SNMP protocol
 engine, the so-called snmpEngineID [RFC3411].  While an appropriate
 snmpEngineID can in principle be configured on each management
 application for each SNMP agent, it is often desirable to discover
 the snmpEngineID automatically.
 This document introduces a discovery mechanism that can be used to
 learn the snmpEngineID of a remote SNMP protocol engine.  The
 proposed mechanism is independent of the features provided by SNMP
 security models.  The mechanism has been designed to coexist with
 discovery mechanisms that may exist in SNMP security models, such as
 the authoritative engine identifier discovery of the User-based
 Security Model (USM) of SNMP [RFC3414].
 This document updates RFC 3411 [RFC3411] by clarifying the IANA rules
 for the maintenance of the SnmpEngineID format registry.
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in RFC 2119 [RFC2119].

2. Background

 Within an administrative domain, an SNMP engine is uniquely
 identified by an snmpEngineID value [RFC3411].  An SNMP entity, which
 consists of an SNMP engine and several SNMP applications, may provide
 access to multiple contexts.
 An SNMP context is a collection of management information accessible
 by an SNMP entity.  An item of management information may exist in
 more than one context and an SNMP entity potentially has access to
 many contexts [RFC3411].  A context is identified by the snmpEngineID
 value of the entity hosting the management information (also called a
 contextEngineID) and a context name that identifies the specific
 context (also called a contextName).
 To identify an individual item of management information within an
 administrative domain, a four tuple is used consisting of
 1.  a contextEngineID,
 2.  a contextName,

Schoenwaelder Standards Track [Page 2] RFC 5343 SNMP Context EngineID Discovery September 2008

 3.  an object type, and
 4.  its instance identification.
 The last two elements are encoded in an object identifier (OID)
 value.  The contextName is a character string (following the
 SnmpAdminString textual convention of the SNMP-FRAMEWORK-MIB
 [RFC3411]) while the contextEngineID is an octet string constructed
 according to the rules defined as part of the SnmpEngineID textual
 convention of the SNMP-FRAMEWORK-MIB [RFC3411].
 The SNMP protocol operations and the protocol data units (PDUs)
 operate on OIDs and thus deal with object types and instances
 [RFC3416].  The SNMP architecture [RFC3411] introduces the concept of
 a scopedPDU as a data structure containing a contextEngineID, a
 contextName, and a PDU.  The SNMP version 3 (SNMPv3) message format
 uses ScopedPDUs to exchange management information [RFC3412].
 Within the SNMP framework, contextEngineIDs serve as end-to-end
 identifiers.  This becomes important in situations where SNMP proxies
 are deployed to translate between protocol versions or to cross
 middleboxes such as network address translators.  In addition,
 snmpEngineIDs separate the identification of an SNMP engine from the
 transport addresses used to communicate with an SNMP engine.  This
 property can be used to correlate management information easily, even
 in situations where multiple different transports were used to
 retrieve the information or where transport addresses can change
 dynamically.
 To retrieve data from an SNMPv3 agent, it is necessary to know the
 appropriate contextEngineID.  The User-based Security Model (USM) of
 SNMPv3 provides a mechanism to discover the snmpEngineID of the
 remote SNMP engine, since this is needed for security processing
 reasons.  The discovered snmpEngineID can subsequently be used as a
 contextEngineID in a ScopedPDU to access management information local
 to the remote SNMP engine.  Other security models, such as the
 Transport Security Model (TSM) [TSM], lack such a procedure and may
 use the discovery mechanism defined in this memo.

3. Procedure

 The proposed discovery mechanism consists of two parts, namely (i)
 the definition of a special well-known snmpEngineID value, called the
 localEngineID, which always refers to a local default context, and
 (ii) the definition of a procedure to acquire the snmpEngineID scalar
 of the SNMP-FRAMEWORK-MIB [RFC3411] using the special well-known
 local localEngineID value.

Schoenwaelder Standards Track [Page 3] RFC 5343 SNMP Context EngineID Discovery September 2008

3.1. Local EngineID

 An SNMP command responder implementing this specification MUST
 register their pduTypes using the localEngineID snmpEngineID value
 (defined below) by invoking the registerContextEngineID() Abstract
 Service Interface (ASI) defined in RFC 3412 [RFC3412].  This
 registration is done in addition to the normal registration under the
 SNMP engine's snmpEngineID.  This is consistent with the SNMPv3
 specifications since they explicitly allow registration of multiple
 engineIDs and multiple pduTypes [RFC3412].
 The SnmpEngineID textual convention [RFC3411] defines that an
 snmpEngineID value MUST be between 5 and 32 octets long.  This
 specification proposes to use the variable length format 3) of the
 SnmpEngineID textual convention and to allocate the reserved, unused
 format value 6, using the enterprise ID 0 for the localEngineID.  An
 ASN.1 definition for localEngineID would look like this:
             localEngineID OCTET STRING ::= '8000000006'H
 The localEngineID value always provides access to the default context
 of an SNMP engine.  Note that the localEngineID value is intended to
 be used as a special value for the contextEngineID field in the
 ScopedPDU.  It MUST NOT be used as a value to identify an SNMP
 engine; that is, this value MUST NOT be used in the snmpEngineID.0
 scalar [RFC3418] or in the msgAuthoritativeEngineID field in the
 securityParameters of the User-based Security Model (USM) [RFC3414].

3.2. EngineID Discovery

 Discovery of the snmpEngineID is done by sending a Read Class
 protocol operation (see Section 2.8 of [RFC3411]) to retrieve the
 snmpEngineID scalar using the localEngineID defined above as a
 contextEngineID value.  Implementations SHOULD only perform this
 discovery step when it is needed.  In particular, if security models
 are used that already discover the remote snmpEngineID (such as USM),
 then no further discovery is necessary.  The same is true in
 situations where the application already knows a suitable
 snmpEngineID value.
 The procedure to discover the snmpEngineID of a remote SNMP engine
 can be described as follows:
 1.  Check whether a suitable contextEngineID value is already known.
     If yes, use the provided contextEngineID value and stop the
     discovery procedure.

Schoenwaelder Standards Track [Page 4] RFC 5343 SNMP Context EngineID Discovery September 2008

 2.  Check whether the selected security model supports discovery of
     the remote snmpEngineID (e.g., USM with its discovery mechanism).
     If yes, let the security model perform the discovery.  If the
     remote snmpEngineID value has been successfully determined,
     assign it to the contextEngineID and stop the discovery
     procedure.
 3.  Send a Read Class operation to the remote SNMP engine using the
     localEngineID value as the contextEngineID in order to retrieve
     the scalar snmpEngineID.0 of the SNMP-FRAMEWORK-MIB [RFC3411].
     If successful, set the contextEngineID to the retrieved value and
     stop the discovery procedure.
 4.  Return an error indication that a suitable contextEngineID could
     not be discovered.
 The procedure outlined above is an example and can be modified to
 retrieve more variables in step 3, such as the sysObjectID.0 scalar
 or the snmpSetSerialNo.0 scalar of the SNMPv2-MIB [RFC3418].

4. IANA Considerations

 RFC 3411 requested that IANA create a registry for SnmpEngineID
 formats.  However, RFC 3411 did not ask IANA to record the initial
 assignments made by RFC 3411 nor did RFC 3411 spell out the precise
 allocation rules.  To address this issue, the following rules are
 hereby established.
 IANA maintains a registry for SnmpEngineID formats.  The first four
 octets of an SnmpEngineID carry an enterprise number, while the fifth
 octet in a variable length SnmpEngineID value, called the format
 octet, indicates how the following octets are formed.  The following
 format values were allocated in [RFC3411]:
   Format    Description                     References
   -------   -----------                     ----------
        0    reserved, unused                 [RFC3411]
        1    IPv4 address                     [RFC3411]
        2    IPv6 address                     [RFC3411]
        3    MAC address                      [RFC3411]
        4    administratively assigned text   [RFC3411]
        5    administratively assigned octets [RFC3411]
     6-127   reserved, unused                 [RFC3411]
   128-255   enterprise specific              [RFC3411]
 IANA can assign new format values out of the originally assigned and
 reserved number space 1-127.  For new assignments in this number

Schoenwaelder Standards Track [Page 5] RFC 5343 SNMP Context EngineID Discovery September 2008

 space, a specification is required as per [RFC5226].  The number
 space 128-255 is enterprise specific and is not controlled by IANA.
 Per this document, IANA has made the following assignment:
   Format    Description                     References
   -------   -----------                     ----------
        6    local engine                     [RFC5343]

5. Security Considerations

 SNMP version 3 (SNMPv3) provides cryptographic security to protect
 devices from unauthorized access.  This specification recommends use
 of the security services provided by SNMPv3.  In particular, it is
 RECOMMENDED to protect the discovery exchange.
 An snmpEngineID can contain information such as a device's MAC
 address, IPv4 address, IPv6 address, or administratively assigned
 text.  An attacker located behind a router / firewall / network
 address translator may not be able to obtain this information
 directly, and he therefore might discover snmpEngineID values in
 order to obtain this kind of device information.
 In many environments, making snmpEngineID values accessible via a
 security level of noAuthNoPriv will benefit legitimate tools that try
 to algorithmically determine some basic information about a device.
 For this reason, the default View-based Access Control Model (VACM)
 configuration in Appendix A of RFC 3415 [RFC3415] gives noAuthNoPriv
 read access to the snmpEngineID.  Furthermore, the USM discovery
 mechanism defined in RFC 3414 [RFC3414] uses unprotected messages and
 reveals snmpEngineID values.
 In highly secure environments, snmpEngineID values can be protected
 by using the discovery mechanism described in this document together
 with a security model that does not exchange cleartext SNMP messages,
 such as the Transport Security Model (TSM) [TSM].
 The isAccessAllowed() abstract service primitive of the SNMP access
 control subsystem does not take the contextEngineID into account when
 checking access rights [RFC3411].  As a consequence, it is not
 possible to define a special view for context engineID discovery.  A
 request with a localEngineID is thus treated like a request with the
 correct snmpEngineID by the access control subsystem.  This is inline
 with the SNMPv3 design where the authenticated identity is the
 securityName (together with the securityModel and securityLevel
 information), and transport addresses or knowledge of contextEngineID
 values do not impact the access-control decision.

Schoenwaelder Standards Track [Page 6] RFC 5343 SNMP Context EngineID Discovery September 2008

6. Acknowledgments

 Dave Perkins suggested the introduction of a "local" contextEngineID
 during the interim meeting of the ISMS (Integrated Security Model for
 SNMP) working group in Boston, 2006.  Joe Fernandez, David
 Harrington, Dan Romascanu, and Bert Wijnen provided helpful review
 and feedback, which helped to improve this document.

7. References

7.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC3411]  Harrington, D., Presuhn, R., and B. Wijnen, "An
            Architecture for Describing Simple Network Management
            Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
            December 2002.
 [RFC3412]  Case, J., Harrington, D., Presuhn, R., and B. Wijnen,
            "Message Processing and Dispatching for the Simple Network
            Management Protocol (SNMP)", STD 62, RFC 3412,
            December 2002.
 [RFC3414]  Blumenthal, U. and B. Wijnen, "User-based Security Model
            (USM) for version 3 of the Simple Network Management
            Protocol (SNMPv3)", STD 62, RFC 3414, December 2002.
 [RFC3416]  Presuhn, R., "Version 2 of the Protocol Operations for the
            Simple Network Management Protocol (SNMP)", STD 62,
            RFC 3416, December 2002.
 [RFC3418]  Presuhn, R., "Management Information Base (MIB) for the
            Simple Network Management Protocol (SNMP)", STD 62,
            RFC 3418, December 2002.
 [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
            IANA Considerations Section in RFCs", BCP 26, RFC 5226,
            May 2008.

7.2. Informative References

 [RFC3410]  Case, J., Mundy, R., Partain, D., and B. Stewart,
            "Introduction and Applicability Statements for Internet-
            Standard Management Framework", RFC 3410, December 2002.

Schoenwaelder Standards Track [Page 7] RFC 5343 SNMP Context EngineID Discovery September 2008

 [RFC3415]  Wijnen, B., Presuhn, R., and K. McCloghrie, "View-based
            Access Control Model (VACM) for the Simple Network
            Management Protocol (SNMP)", STD 62, RFC 3415,
            December 2002.
 [TSM]      Harrington, D., "Transport Security Model for SNMP", Work
            in Progress, July 2008.

Author's Address

 Juergen Schoenwaelder
 Jacobs University Bremen
 Campus Ring 1
 28725 Bremen
 Germany
 Phone: +49 421 200-3587
 EMail: j.schoenwaelder@jacobs-university.de

Schoenwaelder Standards Track [Page 8] RFC 5343 SNMP Context EngineID Discovery September 2008

Full Copyright Statement

 Copyright (C) The IETF Trust (2008).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

 The IETF takes no position regarding the validity or scope of any
 Intellectual Property Rights or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
 this document or the extent to which any license under such rights
 might or might not be available; nor does it represent that it has
 made any independent effort to identify any such rights.  Information
 on the procedures with respect to rights in RFC documents can be
 found in BCP 78 and BCP 79.
 Copies of IPR disclosures made to the IETF Secretariat and any
 assurances of licenses to be made available, or the result of an
 attempt made to obtain a general license or permission for the use of
 such proprietary rights by implementers or users of this
 specification can be obtained from the IETF on-line IPR repository at
 http://www.ietf.org/ipr.
 The IETF invites any interested party to bring to its attention any
 copyrights, patents or patent applications, or other proprietary
 rights that may cover technology that may be required to implement
 this standard.  Please address the information to the IETF at
 ietf-ipr@ietf.org.

Schoenwaelder Standards Track [Page 9]

Network Working Group D. Harrington Request for Comments: 5590 Huawei Technologies (USA) Updates: 3411, 3412, 3414, 3417 J. Schoenwaelder Category: Standards Track Jacobs University Bremen

                                                             June 2009

Transport Subsystem for the Simple Network Management Protocol (SNMP)

Status of This Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (c) 2009 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents in effect on the date of
 publication of this document (http://trustee.ietf.org/license-info).
 Please review these documents carefully, as they describe your rights
 and restrictions with respect to this document.
 This document may contain material from IETF Documents or IETF
 Contributions published or made publicly available before November
 10, 2008.  The person(s) controlling the copyright in some of this
 material may not have granted the IETF Trust the right to allow
 modifications of such material outside the IETF Standards Process.
 Without obtaining an adequate license from the person(s) controlling
 the copyright in such materials, this document may not be modified
 outside the IETF Standards Process, and derivative works of it may
 not be created outside the IETF Standards Process, except to format
 it for publication as an RFC or to translate it into languages other
 than English.

Abstract

 This document defines a Transport Subsystem, extending the Simple
 Network Management Protocol (SNMP) architecture defined in RFC 3411.
 This document defines a subsystem to contain Transport Models that is
 comparable to other subsystems in the RFC 3411 architecture.  As work
 is being done to expand the transports to include secure transports,
 such as the Secure Shell (SSH) Protocol and Transport Layer Security

Harrington & Schoenwaelder Standards Track [Page 1] RFC 5590 SNMP Transport Subsystem June 2009

 (TLS), using a subsystem will enable consistent design and modularity
 of such Transport Models.  This document identifies and describes
 some key aspects that need to be considered for any Transport Model
 for SNMP.

Table of Contents

 1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   1.1.  The Internet-Standard Management Framework . . . . . . . .  3
   1.2.  Conventions  . . . . . . . . . . . . . . . . . . . . . . .  3
   1.3.  Where This Extension Fits  . . . . . . . . . . . . . . . .  4
 2.  Motivation . . . . . . . . . . . . . . . . . . . . . . . . . .  5
 3.  Requirements of a Transport Model  . . . . . . . . . . . . . .  7
   3.1.  Message Security Requirements  . . . . . . . . . . . . . .  7
     3.1.1.  Security Protocol Requirements . . . . . . . . . . . .  7
   3.2.  SNMP Requirements  . . . . . . . . . . . . . . . . . . . .  8
     3.2.1.  Architectural Modularity Requirements  . . . . . . . .  8
     3.2.2.  Access Control Requirements  . . . . . . . . . . . . . 11
     3.2.3.  Security Parameter Passing Requirements  . . . . . . . 12
     3.2.4.  Separation of Authentication and Authorization . . . . 12
   3.3.  Session Requirements . . . . . . . . . . . . . . . . . . . 13
     3.3.1.  No SNMP Sessions . . . . . . . . . . . . . . . . . . . 13
     3.3.2.  Session Establishment Requirements . . . . . . . . . . 14
     3.3.3.  Session Maintenance Requirements . . . . . . . . . . . 15
     3.3.4.  Message Security versus Session Security . . . . . . . 15
 4.  Scenario Diagrams and the Transport Subsystem  . . . . . . . . 16
 5.  Cached Information and References  . . . . . . . . . . . . . . 17
   5.1.  securityStateReference . . . . . . . . . . . . . . . . . . 17
   5.2.  tmStateReference . . . . . . . . . . . . . . . . . . . . . 17
     5.2.1.  Transport Information  . . . . . . . . . . . . . . . . 18
     5.2.2.  securityName . . . . . . . . . . . . . . . . . . . . . 19
     5.2.3.  securityLevel  . . . . . . . . . . . . . . . . . . . . 20
     5.2.4.  Session Information  . . . . . . . . . . . . . . . . . 20
 6.  Abstract Service Interfaces  . . . . . . . . . . . . . . . . . 21
   6.1.  sendMessage ASI  . . . . . . . . . . . . . . . . . . . . . 21
   6.2.  Changes to RFC 3411 Outgoing ASIs  . . . . . . . . . . . . 22
     6.2.1.  Message Processing Subsystem Primitives  . . . . . . . 22
     6.2.2.  Security Subsystem Primitives  . . . . . . . . . . . . 23
   6.3.  The receiveMessage ASI . . . . . . . . . . . . . . . . . . 24
   6.4.  Changes to RFC 3411 Incoming ASIs  . . . . . . . . . . . . 25
     6.4.1.  Message Processing Subsystem Primitive . . . . . . . . 25
     6.4.2.  Security Subsystem Primitive . . . . . . . . . . . . . 26
 7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 27
   7.1.  Coexistence, Security Parameters, and Access Control . . . 27
 8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 29
 9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 29
 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 30
   10.1. Normative References . . . . . . . . . . . . . . . . . . . 30

Harrington & Schoenwaelder Standards Track [Page 2] RFC 5590 SNMP Transport Subsystem June 2009

   10.2. Informative References . . . . . . . . . . . . . . . . . . 30
 Appendix A.  Why tmStateReference? . . . . . . . . . . . . . . . . 32
   A.1.  Define an Abstract Service Interface . . . . . . . . . . . 32
   A.2.  Using an Encapsulating Header  . . . . . . . . . . . . . . 32
   A.3.  Modifying Existing Fields in an SNMP Message . . . . . . . 32
   A.4.  Using a Cache  . . . . . . . . . . . . . . . . . . . . . . 33

1. Introduction

 This document defines a Transport Subsystem, extending the Simple
 Network Management Protocol (SNMP) architecture defined in [RFC3411].
 This document identifies and describes some key aspects that need to
 be considered for any Transport Model for SNMP.

1.1. The Internet-Standard Management Framework

 For a detailed overview of the documents that describe the current
 Internet-Standard Management Framework, please refer to Section 7 of
 RFC 3410 [RFC3410].

1.2. Conventions

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in RFC 2119 [RFC2119].
 Lowercase versions of the keywords should be read as in normal
 English.  They will usually, but not always, be used in a context
 that relates to compatibility with the RFC 3411 architecture or the
 subsystem defined here but that might have no impact on on-the-wire
 compatibility.  These terms are used as guidance for designers of
 proposed IETF models to make the designs compatible with RFC 3411
 subsystems and Abstract Service Interfaces (ASIs).  Implementers are
 free to implement differently.  Some usages of these lowercase terms
 are simply normal English usage.
 For consistency with SNMP-related specifications, this document
 favors terminology as defined in STD 62, rather than favoring
 terminology that is consistent with non-SNMP specifications that use
 different variations of the same terminology.  This is consistent
 with the IESG decision to not require the SNMPv3 terminology be
 modified to match the usage of other non-SNMP specifications when
 SNMPv3 was advanced to Full Standard.
 This document discusses an extension to the modular RFC 3411
 architecture; this is not a protocol document.  An architectural
 "MUST" is a really sharp constraint; to allow for the evolution of
 technology and to not unnecessarily constrain future models, often a

Harrington & Schoenwaelder Standards Track [Page 3] RFC 5590 SNMP Transport Subsystem June 2009

 "SHOULD" or a "should" is more appropriate than a "MUST" in an
 architecture.  Future models MAY express tighter requirements for
 their own model-specific processing.

1.3. Where This Extension Fits

 It is expected that readers of this document will have read RFCs 3410
 and 3411, and have a general understanding of the functionality
 defined in RFCs 3412-3418.
 The "Transport Subsystem" is an additional component for the SNMP
 Engine depicted in RFC 3411, Section 3.1.
 The following diagram depicts its place in the RFC 3411 architecture.
 +-------------------------------------------------------------------+
 |  SNMP entity                                                      |
 |                                                                   |
 |  +-------------------------------------------------------------+  |
 |  |  SNMP engine (identified by snmpEngineID)                   |  |
 |  |                                                             |  |
 |  |  +------------+                                             |  |
 |  |  | Transport  |                                             |  |
 |  |  | Subsystem  |                                             |  |
 |  |  +------------+                                             |  |
 |  |                                                             |  |
 |  |  +------------+ +------------+ +-----------+ +-----------+  |  |
 |  |  | Dispatcher | | Message    | | Security  | | Access    |  |  |
 |  |  |            | | Processing | | Subsystem | | Control   |  |  |
 |  |  |            | | Subsystem  | |           | | Subsystem |  |  |
 |  |  +------------+ +------------+ +-----------+ +-----------+  |  |
 |  +-------------------------------------------------------------+  |
 |                                                                   |
 |  +-------------------------------------------------------------+  |
 |  |  Application(s)                                             |  |
 |  |                                                             |  |
 |  |  +-------------+  +--------------+  +--------------+        |  |
 |  |  | Command     |  | Notification |  | Proxy        |        |  |
 |  |  | Generator   |  | Receiver     |  | Forwarder    |        |  |
 |  |  +-------------+  +--------------+  +--------------+        |  |
 |  |                                                             |  |
 |  |  +-------------+  +--------------+  +--------------+        |  |
 |  |  | Command     |  | Notification |  | Other        |        |  |
 |  |  | Responder   |  | Originator   |  |              |        |  |
 |  |  +-------------+  +--------------+  +--------------+        |  |
 |  +-------------------------------------------------------------+  |
 |                                                                   |
 +-------------------------------------------------------------------+

Harrington & Schoenwaelder Standards Track [Page 4] RFC 5590 SNMP Transport Subsystem June 2009

 The transport mappings defined in RFC 3417 do not provide lower-layer
 security functionality, and thus do not provide transport-specific
 security parameters.  This document updates RFC 3411 and RFC 3417 by
 defining an architectural extension and modifying the ASIs that
 transport mappings (hereafter called "Transport Models") can use to
 pass transport-specific security parameters to other subsystems,
 including transport-specific security parameters that are translated
 into the transport-independent securityName and securityLevel
 parameters.
 The Transport Security Model [RFC5591] and the Secure Shell Transport
 Model [RFC5592] utilize the Transport Subsystem.  The Transport
 Security Model is an alternative to the existing SNMPv1 Security
 Model [RFC3584], the SNMPv2c Security Model [RFC3584], and the User-
 based Security Model [RFC3414].  The Secure Shell Transport Model is
 an alternative to existing transport mappings as described in
 [RFC3417].

2. Motivation

 Just as there are multiple ways to secure one's home or business, in
 a continuum of alternatives, there are multiple ways to secure a
 network management protocol.  Let's consider three general
 approaches.
 In the first approach, an individual could sit on his front porch
 waiting for intruders.  In the second approach, he could hire an
 employee, schedule the employee, position the employee to guard what
 he wants protected, hire a second guard to cover if the first gets
 sick, and so on.  In the third approach, he could hire a security
 company, tell them what he wants protected, and leave the details to
 them.  Considerations of hiring and training employees, positioning
 and scheduling the guards, arranging for cover, etc., are the
 responsibility of the security company.  The individual therefore
 achieves the desired security, with significantly less effort on his
 part except for identifying requirements and verifying the quality of
 service being provided.
 The User-based Security Model (USM) as defined in [RFC3414] largely
 uses the first approach -- it provides its own security.  It utilizes
 existing mechanisms (e.g., SHA), but provides all the coordination.
 USM provides for the authentication of a principal, message
 encryption, data integrity checking, timeliness checking, etc.
 USM was designed to be independent of other existing security
 infrastructures.  USM therefore uses a separate principal and key
 management infrastructure.  Operators have reported that deploying
 another principal and key management infrastructure in order to use

Harrington & Schoenwaelder Standards Track [Page 5] RFC 5590 SNMP Transport Subsystem June 2009

 SNMPv3 is a deterrent to deploying SNMPv3.  It is possible to use
 external mechanisms to handle the distribution of keys for use by
 USM.  The more important issue is that operators wanted to leverage
 existing user management infrastructures that were not specific to
 SNMP.
 A USM-compliant architecture might combine the authentication
 mechanism with an external mechanism, such as RADIUS [RFC2865], to
 provide the authentication service.  Similarly, it might be possible
 to utilize an external protocol to encrypt a message, to check
 timeliness, to check data integrity, etc.  However, this corresponds
 to the second approach -- requiring the coordination of a number of
 differently subcontracted services.  Building solid security between
 the various services is difficult, and there is a significant
 potential for gaps in security.
 An alternative approach might be to utilize one or more lower-layer
 security mechanisms to provide the message-oriented security services
 required.  These would include authentication of the sender,
 encryption, timeliness checking, and data integrity checking.  This
 corresponds to the third approach described above.  There are a
 number of IETF standards available or in development to address these
 problems through security layers at the transport layer or
 application layer, among them are TLS [RFC5246], Simple
 Authentication and Security Layer (SASL) [RFC4422], and SSH [RFC4251]
 From an operational perspective, it is highly desirable to use
 security mechanisms that can unify the administrative security
 management for SNMPv3, command line interfaces (CLIs), and other
 management interfaces.  The use of security services provided by
 lower layers is the approach commonly used for the CLI, and is also
 the approach being proposed for other network management protocols,
 such as syslog [RFC5424] and NETCONF [RFC4741].
 This document defines a Transport Subsystem extension to the RFC 3411
 architecture that is based on the third approach.  This extension
 specifies how other lower-layer protocols with common security
 infrastructures can be used underneath the SNMP protocol and the
 desired goal of unified administrative security can be met.
 This extension allows security to be provided by an external protocol
 connected to the SNMP engine through an SNMP Transport Model
 [RFC3417].  Such a Transport Model would then enable the use of
 existing security mechanisms, such as TLS [RFC5246] or SSH [RFC4251],
 within the RFC 3411 architecture.

Harrington & Schoenwaelder Standards Track [Page 6] RFC 5590 SNMP Transport Subsystem June 2009

 There are a number of Internet security protocols and mechanisms that
 are in widespread use.  Many of them try to provide a generic
 infrastructure to be used by many different application-layer
 protocols.  The motivation behind the Transport Subsystem is to
 leverage these protocols where it seems useful.
 There are a number of challenges to be addressed to map the security
 provided by a secure transport into the SNMP architecture so that
 SNMP continues to provide interoperability with existing
 implementations.  These challenges are described in detail in this
 document.  For some key issues, design choices are described that
 might be made to provide a workable solution that meets operational
 requirements and fits into the SNMP architecture defined in
 [RFC3411].

3. Requirements of a Transport Model

3.1. Message Security Requirements

 Transport security protocols SHOULD provide protection against the
 following message-oriented threats:
 1.  modification of information
 2.  masquerade
 3.  message stream modification
 4.  disclosure
 These threats are described in Section 1.4 of [RFC3411].  The
 security requirements outlined there do not require protection
 against denial of service or traffic analysis; however, transport
 security protocols should not make those threats significantly worse.

3.1.1. Security Protocol Requirements

 There are a number of standard protocols that could be proposed as
 possible solutions within the Transport Subsystem.  Some factors
 should be considered when selecting a protocol.
 Using a protocol in a manner for which it was not designed has
 numerous problems.  The advertised security characteristics of a
 protocol might depend on it being used as designed; when used in
 other ways, it might not deliver the expected security
 characteristics.  It is recommended that any proposed model include a
 description of the applicability of the Transport Model.

Harrington & Schoenwaelder Standards Track [Page 7] RFC 5590 SNMP Transport Subsystem June 2009

 A Transport Model SHOULD NOT require modifications to the underlying
 protocol.  Modifying the protocol might change its security
 characteristics in ways that could impact other existing usages.  If
 a change is necessary, the change SHOULD be an extension that has no
 impact on the existing usages.  Any Transport Model specification
 should include a description of potential impact on other usages of
 the protocol.
 Since multiple Transport Models can exist simultaneously within the
 Transport Subsystem, Transport Models MUST be able to coexist with
 each other.

3.2. SNMP Requirements

3.2.1. Architectural Modularity Requirements

 SNMP version 3 (SNMPv3) is based on a modular architecture (defined
 in Section 3 of [RFC3411]) to allow the evolution of the SNMP
 protocol standards over time and to minimize the side effects between
 subsystems when changes are made.
 The RFC 3411 architecture includes a Message Processing Subsystem for
 permitting different message versions to be handled by a single
 engine, a Security Subsystem for enabling different methods of
 providing security services, Applications to support different types
 of Application processors, and an Access Control Subsystem for
 allowing multiple approaches to access control.  The RFC 3411
 architecture does not include a subsystem for Transport Models,
 despite the fact there are multiple transport mappings already
 defined for SNMP [RFC3417].  This document describes a Transport
 Subsystem that is compatible with the RFC 3411 architecture.  As work
 is being done to use secure transports such as SSH and TLS, using a
 subsystem will enable consistent design and modularity of such
 Transport Models.
 The design of this Transport Subsystem accepts the goals of the RFC
 3411 architecture that are defined in Section 1.5 of [RFC3411].  This
 Transport Subsystem uses a modular design that permits Transport
 Models (which might or might not be security-aware) to be "plugged
 into" the RFC 3411 architecture.  Such Transport Models would be
 independent of other modular SNMP components as much as possible.
 This design also permits Transport Models to be advanced through the
 standards process independently of other Transport Models.
 The following diagram depicts the SNMPv3 architecture, including the
 new Transport Subsystem defined in this document and a new Transport
 Security Model defined in [RFC5591].

Harrington & Schoenwaelder Standards Track [Page 8] RFC 5590 SNMP Transport Subsystem June 2009

 +------------------------------+
 |    Network                   |
 +------------------------------+
    ^       ^              ^
    |       |              |
    v       v              v
 +-------------------------------------------------------------------+
 | +--------------------------------------------------+              |
 | |  Transport Subsystem                             |              |
 | | +-----+ +-----+ +-----+ +-----+       +-------+  |              |
 | | | UDP | | TCP | | SSH | | TLS | . . . | other |  |              |
 | | +-----+ +-----+ +-----+ +-----+       +-------+  |              |
 | +--------------------------------------------------+              |
 |              ^                                                    |
 |              |                                                    |
 | Dispatcher   v                                                    |
 | +-------------------+ +---------------------+  +----------------+ |
 | | Transport         | | Message Processing  |  | Security       | |
 | | Dispatch          | | Subsystem           |  | Subsystem      | |
 | |                   | |     +------------+  |  | +------------+ | |
 | |                   | |  +->| v1MP       |<--->| | USM        | | |
 | |                   | |  |  +------------+  |  | +------------+ | |
 | |                   | |  |  +------------+  |  | +------------+ | |
 | |                   | |  +->| v2cMP      |<--->| | Transport  | | |
 | | Message           | |  |  +------------+  |  | | Security   | | |
 | | Dispatch    <--------->|  +------------+  |  | | Model      | | |
 | |                   | |  +->| v3MP       |<--->| +------------+ | |
 | |                   | |  |  +------------+  |  | +------------+ | |
 | | PDU Dispatch      | |  |  +------------+  |  | | Other      | | |
 | +-------------------+ |  +->| otherMP    |<--->| | Model(s)   | | |
 |              ^        |     +------------+  |  | +------------+ | |
 |              |        +---------------------+  +----------------+ |
 |              v                                                    |
 |      +-------+-------------------------+---------------+          |
 |      ^                                 ^               ^          |
 |      |                                 |               |          |
 |      v                                 v               v          |
 | +-------------+   +---------+   +--------------+  +-------------+ |
 | |   COMMAND   |   | ACCESS  |   | NOTIFICATION |  |    PROXY    | |
 | |  RESPONDER  |<->| CONTROL |<->|  ORIGINATOR  |  |  FORWARDER  | |
 | | Application |   |         |   | Applications |  | Application | |
 | +-------------+   +---------+   +--------------+  +-------------+ |
 |      ^                                 ^                          |
 |      |                                 |                          |
 |      v                                 v                          |
 | +----------------------------------------------+                  |
 | |             MIB instrumentation              |      SNMP entity |
 +-------------------------------------------------------------------+

Harrington & Schoenwaelder Standards Track [Page 9] RFC 5590 SNMP Transport Subsystem June 2009

3.2.1.1. Changes to the RFC 3411 Architecture

 The RFC 3411 architecture and the Security Subsystem assume that a
 Security Model is called by a Message Processing Model and will
 perform multiple security functions within the Security Subsystem.  A
 Transport Model that supports a secure transport protocol might
 perform similar security functions within the Transport Subsystem,
 including the translation of transport-security parameters to/from
 Security-Model-independent parameters.
 To accommodate this, an implementation-specific cache of transport-
 specific information will be described (not shown), and the data
 flows on this path will be extended to pass Security-Model-
 independent values.  This document amends some of the ASIs defined in
 RFC 3411; these changes are covered in Section 6 of this document.
 New Security Models might be defined that understand how to work with
 these modified ASIs and the transport-information cache.  One such
 Security Model, the Transport Security Model, is defined in
 [RFC5591].

3.2.1.2. Changes to RFC 3411 Processing

 The introduction of secure transports affects the responsibilities
 and order of processing within the RFC 3411 architecture.  While the
 steps are the same, they might occur in a different order, and might
 be done by different subsystems.  With the existing RFC 3411
 architecture, security processing starts when the Message Processing
 Model decodes portions of the encoded message to extract parameters
 that identify which Security Model MUST handle the security-related
 tasks.
 A secure transport performs those security functions on the message,
 before the message is decoded.  Some of these functions might then be
 repeated by the selected Security Model.

3.2.1.3. Passing Information between SNMP Engines

 A secure Transport Model will establish an authenticated and possibly
 encrypted tunnel between the Transport Models of two SNMP engines.
 After a transport-layer tunnel is established, then SNMP messages can
 be sent through the tunnel from one SNMP engine to the other.  While
 the Community Security Models [RFC3584] and the User-based Security
 Model establish a security association for each SNMP message, newer
 Transport Models MAY support sending multiple SNMP messages through
 the same tunnel to amortize the costs of establishing a security
 association.

Harrington & Schoenwaelder Standards Track [Page 10] RFC 5590 SNMP Transport Subsystem June 2009

3.2.2. Access Control Requirements

 RFC 3411 made some design decisions related to the support of an
 Access Control Subsystem.  These include establishing and passing in
 a model-independent manner the securityModel, securityName, and
 securityLevel parameters, and separating message authentication from
 data-access authorization.

3.2.2.1. securityName and securityLevel Mapping

 SNMP data-access controls are expected to work on the basis of who
 can perform what operations on which subsets of data, and based on
 the security services that will be provided to secure the data in
 transit.  The securityModel and securityLevel parameters establish
 the protections for transit -- whether authentication and privacy
 services will be or have been applied to the message.  The
 securityName is a model-independent identifier of the security
 "principal".
 A Security Model plays a role in security that goes beyond protecting
 the message -- it provides a mapping between the Security-Model-
 specific principal for an incoming message to a Security-Model
 independent securityName that can be used for subsequent processing,
 such as for access control.  The securityName is mapped from a
 mechanism-specific identity, and this mapping must be done for
 incoming messages by the Security Model before it passes securityName
 to the Message Processing Model via the processIncoming ASI.
 A Security Model is also responsible to specify, via the
 securityLevel parameter, whether incoming messages have been
 authenticated and encrypted, and to ensure that outgoing messages are
 authenticated and encrypted based on the value of securityLevel.
 A Transport Model MAY provide suggested values for securityName and
 securityLevel.  A Security Model might have multiple sources for
 determining the principal and desired security services, and a
 particular Security Model might or might not utilize the values
 proposed by a Transport Model when deciding the value of securityName
 and securityLevel.
 Documents defining a new transport domain MUST define a prefix that
 MAY be prepended to all securityNames passed by the Security Model.
 The prefix MUST include one to four US-ASCII alpha-numeric
 characters, not including a ":" (US-ASCII 0x3a) character.  If a
 prefix is used, a securityName is constructed by concatenating the
 prefix and a ":" (US-ASCII 0x3a) character, followed by a non-empty
 identity in an snmpAdminString-compatible format.  The prefix can be
 used by SNMP Applications to distinguish "alice" authenticated by SSH

Harrington & Schoenwaelder Standards Track [Page 11] RFC 5590 SNMP Transport Subsystem June 2009

 from "alice" authenticated by TLS.  Transport domains and their
 corresponding prefixes are coordinated via the IANA registry "SNMP
 Transport Domains".

3.2.3. Security Parameter Passing Requirements

 A Message Processing Model might unpack SNMP-specific security
 parameters from an incoming message before calling a specific
 Security Model to handle the security-related processing of the
 message.  When using a secure Transport Model, some security
 parameters might be extracted from the transport layer by the
 Transport Model before the message is passed to the Message
 Processing Subsystem.
 This document describes a cache mechanism (see Section 5) into which
 the Transport Model puts information about the transport and security
 parameters applied to a transport connection or an incoming message;
 a Security Model might extract that information from the cache.  A
 tmStateReference is passed as an extra parameter in the ASIs between
 the Transport Subsystem and the Message Processing and Security
 Subsystems in order to identify the relevant cache.  This approach of
 passing a model-independent reference is consistent with the
 securityStateReference cache already being passed around in the RFC
 3411 ASIs.

3.2.4. Separation of Authentication and Authorization

 The RFC 3411 architecture defines a separation of authentication and
 the authorization to access and/or modify MIB data.  A set of model-
 independent parameters (securityModel, securityName, and
 securityLevel) are passed between the Security Subsystem, the
 Applications, and the Access Control Subsystem.
 This separation was a deliberate decision of the SNMPv3 WG, in order
 to allow support for authentication protocols that do not provide
 data-access authorization capabilities, and in order to support data-
 access authorization schemes, such as the View-based access Control
 Model (VACM), that do not perform their own authentication.
 A Message Processing Model determines which Security Model is used,
 either based on the message version (e.g., SNMPv1 and SNMPv2c) or
 possibly by a value specified in the message (e.g., msgSecurityModel
 field in SNMPv3).
 The Security Model makes the decision which securityName and
 securityLevel values are passed as model-independent parameters to an
 Application, which then passes them via the isAccessAllowed ASI to
 the Access Control Subsystem.

Harrington & Schoenwaelder Standards Track [Page 12] RFC 5590 SNMP Transport Subsystem June 2009

 An Access Control Model performs the mapping from the model-
 independent security parameters to a policy within the Access Control
 Model that is Access-Control-Model-dependent.
 A Transport Model does not know which Security Model will be used for
 an incoming message, and so cannot know how the securityName and
 securityLevel parameters will be determined.  It can propose an
 authenticated identity (via the tmSecurityName field), but there is
 no guarantee that this value will be used by the Security Model.  For
 example, non-transport-aware Security Models will typically determine
 the securityName (and securityLevel) based on the contents of the
 SNMP message itself.  Such Security Models will simply not know that
 the tmStateReference cache exists.
 Further, even if the Transport Model can influence the choice of
 securityName, it cannot directly determine the authorization allowed
 to this identity.  If two different Transport Models each
 authenticate a transport principal that are then both mapped to the
 same securityName, then these two identities will typically be
 afforded exactly the same authorization by the Access Control Model.
 The only way for the Access Control Model to differentiate between
 identities based on the underlying Transport Model would be for such
 transport-authenticated identities to be mapped to distinct
 securityNames.  How and if this is done is Security-Model-dependent.

3.3. Session Requirements

 Some secure transports have a notion of sessions, while other secure
 transports provide channels or other session-like mechanisms.
 Throughout this document, the term "session" is used in a broad sense
 to cover transport sessions, transport channels, and other transport-
 layer, session-like mechanisms.  Transport-layer sessions that can
 secure multiple SNMP messages within the lifetime of the session are
 considered desirable because the cost of authentication can be
 amortized over potentially many transactions.  How a transport
 session is actually established, opened, closed, or maintained is
 specific to a particular Transport Model.
 To reduce redundancy, this document describes aspects that are
 expected to be common to all Transport Model sessions.

3.3.1. No SNMP Sessions

 The architecture defined in [RFC3411] and the Transport Subsystem
 defined in this document do not support SNMP sessions or include a
 session selector in the Abstract Service Interfaces.

Harrington & Schoenwaelder Standards Track [Page 13] RFC 5590 SNMP Transport Subsystem June 2009

 The Transport Subsystem might support transport sessions.  However,
 the Transport Subsystem does not have access to the pduType (i.e.,
 the SNMP operation type), and so cannot select a given transport
 session for particular types of traffic.
 Certain parameters of the Abstract Service Interfaces might be used
 to guide the selection of an appropriate transport session to use for
 a given request by an Application.
 The transportDomain and transportAddress identify the transport
 connection to a remote network node.  Elements of the transport
 address (such as the port number) might be used by an Application to
 send a particular PDU type to a particular transport address.  For
 example, the SNMP-TARGET-MIB and SNMP-NOTIFICATION-MIB [RFC3413] are
 used to configure notification originators with the destination port
 to which SNMPv2-Trap PDUs or Inform PDUs are to be sent, but the
 Transport Subsystem never looks inside the PDU.
 The securityName identifies which security principal to communicate
 with at that address (e.g., different Network Management System (NMS)
 applications), and the securityLevel might permit selection of
 different sets of security properties for different purposes (e.g.,
 encrypted SET vs. non-encrypted GET operations).
 However, because the handling of transport sessions is specific to
 each Transport Model, some Transport Models MAY restrict selecting a
 particular transport session.  A user application might use a unique
 combination of transportDomain, transportAddress, securityModel,
 securityName, and securityLevel to try to force the selection of a
 given transport session.  This usage is NOT RECOMMENDED because it is
 not guaranteed to be interoperable across implementations and across
 models.
 Implementations SHOULD be able to maintain some reasonable number of
 concurrent transport sessions, and MAY provide non-standard internal
 mechanisms to select transport sessions.

3.3.2. Session Establishment Requirements

 SNMP Applications provide the transportDomain, transportAddress,
 securityName, and securityLevel to be used to create a new session.
 If the Transport Model cannot provide at least the requested level of
 security, the Transport Model should discard the message and should
 notify the Dispatcher that establishing a session and sending the
 message failed.  Similarly, if the session cannot be established,
 then the message should be discarded and the Dispatcher notified.

Harrington & Schoenwaelder Standards Track [Page 14] RFC 5590 SNMP Transport Subsystem June 2009

 Transport session establishment might require provisioning
 authentication credentials at an engine, either statically or
 dynamically.  How this is done is dependent on the Transport Model
 and the implementation.

3.3.3. Session Maintenance Requirements

 A Transport Model can tear down sessions as needed.  It might be
 necessary for some implementations to tear down sessions as the
 result of resource constraints, for example.
 The decision to tear down a session is implementation-dependent.  How
 an implementation determines that an operation has completed is
 implementation-dependent.  While it is possible to tear down each
 transport session after processing for each message has completed,
 this is not recommended for performance reasons.
 The elements of procedure describe when cached information can be
 discarded, and the timing of cache cleanup might have security
 implications, but cache memory management is an implementation issue.
 If a Transport Model defines MIB module objects to maintain session
 state information, then the Transport Model MUST define what happens
 to the objects when a related session is torn down, since this will
 impact the interoperability of the MIB module.

3.3.4. Message Security versus Session Security

 A Transport Model session is associated with state information that
 is maintained for its lifetime.  This state information allows for
 the application of various security services to multiple messages.
 Cryptographic keys associated with the transport session SHOULD be
 used to provide authentication, integrity checking, and encryption
 services, as needed, for data that is communicated during the
 session.  The cryptographic protocols used to establish keys for a
 Transport Model session SHOULD ensure that fresh new session keys are
 generated for each session.  This would ensure that a cross-session
 replay attack would be unsuccessful; that is, an attacker could not
 take a message observed on one session and successfully replay it on
 another session.
 A good security protocol would also protect against replay attacks
 within a session; that is, an attacker could not take a message
 observed on a session and successfully replay it later in the same
 session.  One approach would be to use sequence information within
 the protocol, allowing the participants to detect if messages were
 replayed or reordered within a session.

Harrington & Schoenwaelder Standards Track [Page 15] RFC 5590 SNMP Transport Subsystem June 2009

 If a secure transport session is closed between the time a request
 message is received and the corresponding response message is sent,
 then the response message SHOULD be discarded, even if a new session
 has been established.  The SNMPv3 WG decided that this should be a
 "SHOULD" architecturally, and it is a Security-Model-specific
 decision whether to REQUIRE this.  The architecture does not mandate
 this requirement in order to allow for future Security Models where
 this might make sense; however, not requiring this could lead to
 added complexity and security vulnerabilities, so most Security
 Models SHOULD require this.
 SNMPv3 was designed to support multiple levels of security,
 selectable on a per-message basis by an SNMP Application, because,
 for example, there is not much value in using encryption for a
 command generator to poll for potentially non-sensitive performance
 data on thousands of interfaces every ten minutes; such encryption
 might add significant overhead to processing of the messages.
 Some Transport Models might support only specific authentication and
 encryption services, such as requiring all messages to be carried
 using both authentication and encryption, regardless of the security
 level requested by an SNMP Application.  A Transport Model MAY
 upgrade the security level requested by a transport-aware Security
 Model, i.e., noAuthNoPriv and authNoPriv might be sent over an
 authenticated and encrypted session.  A Transport Model MUST NOT
 downgrade the security level requested by a transport-aware Security
 Model, and SHOULD discard any message where this would occur.  This
 is a SHOULD rather than a MUST only to permit the potential
 development of models that can perform error-handling in a manner
 that is less severe than discarding the message.  However, any model
 that does not discard the message in this circumstance should have a
 clear justification for why not discarding will not create a security
 vulnerability.

4. Scenario Diagrams and the Transport Subsystem

 Sections 4.6.1 and 4.6.2 of RFC 3411 provide scenario diagrams to
 illustrate how an outgoing message is created and how an incoming
 message is processed.  RFC 3411 does not define ASIs for the "Send
 SNMP Request Message to Network", "Receive SNMP Response Message from
 Network", "Receive SNMP Message from Network" and "Send SNMP message
 to Network" arrows in these diagrams.
 This document defines two ASIs corresponding to these arrows: a
 sendMessage ASI to send SNMP messages to the network and a
 receiveMessage ASI to receive SNMP messages from the network.  These
 ASIs are used for all SNMP messages, regardless of pduType.

Harrington & Schoenwaelder Standards Track [Page 16] RFC 5590 SNMP Transport Subsystem June 2009

5. Cached Information and References

 When performing SNMP processing, there are two levels of state
 information that might need to be retained: the immediate state
 linking a request-response pair and a potentially longer-term state
 relating to transport and security.
 The RFC 3411 architecture uses caches to maintain the short-term
 message state, and uses references in the ASIs to pass this
 information between subsystems.
 This document defines the requirements for a cache to handle
 additional short-term message state and longer-term transport state
 information, using a tmStateReference parameter to pass this
 information between subsystems.
 To simplify the elements of procedure, the release of state
 information is not always explicitly specified.  As a general rule,
 if state information is available when a message being processed gets
 discarded, the state related to that message should also be
 discarded.  If state information is available when a relationship
 between engines is severed, such as the closing of a transport
 session, the state information for that relationship should also be
 discarded.
 Since the contents of a cache are meaningful only within an
 implementation, and not on-the-wire, the format of the cache is
 implementation-specific.

5.1. securityStateReference

 The securityStateReference parameter is defined in RFC 3411.  Its
 primary purpose is to provide a mapping between a request and the
 corresponding response.  This cache is not accessible to Transport
 Models, and an entry is typically only retained for the lifetime of a
 request-response pair of messages.

5.2. tmStateReference

 For each transport session, information about the transport security
 is stored in a tmState cache or datastore that is referenced by a
 tmStateReference.  The tmStateReference parameter is used to pass
 model-specific and mechanism-specific parameters between the
 Transport Subsystem and transport-aware Security Models.
 In general, when necessary, the tmState is populated by the Security
 Model for outgoing messages and by the Transport Model for incoming
 messages.  However, in both cases, the model populating the tmState

Harrington & Schoenwaelder Standards Track [Page 17] RFC 5590 SNMP Transport Subsystem June 2009

 might have incomplete information, and the missing information might
 be populated by the other model when the information becomes
 available.
 The tmState might contain both long-term and short-term information.
 The session information typically remains valid for the duration of
 the transport session, might be used for several messages, and might
 be stored in a local configuration datastore.  Some information has a
 shorter lifespan, such as tmSameSecurity and
 tmRequestedSecurityLevel, which are associated with a specific
 message.
 Since this cache is only used within an implementation, and not on-
 the-wire, the precise contents and format of the cache are
 implementation-dependent.  For architectural modularity between
 Transport Models and transport-aware Security Models, a fully-defined
 tmState MUST conceptually include at least the following fields:
    tmTransportDomain
    tmTransportAddress
    tmSecurityName
    tmRequestedSecurityLevel
    tmTransportSecurityLevel
    tmSameSecurity
    tmSessionID
 The details of these fields are described in the following
 subsections.

5.2.1. Transport Information

 Information about the source of an incoming SNMP message is passed up
 from the Transport Subsystem as far as the Message Processing
 Subsystem.  However, these parameters are not included in the
 processIncomingMsg ASI defined in RFC 3411; hence, this information
 is not directly available to the Security Model.
 A transport-aware Security Model might wish to take account of the
 transport protocol and originating address when authenticating the
 request and setting up the authorization parameters.  It is therefore

Harrington & Schoenwaelder Standards Track [Page 18] RFC 5590 SNMP Transport Subsystem June 2009

 necessary for the Transport Model to include this information in the
 tmStateReference cache so that it is accessible to the Security
 Model.
 o  tmTransportDomain: the transport protocol (and hence the Transport
    Model) used to receive the incoming message.
 o  tmTransportAddress: the source of the incoming message.
 The ASIs used for processing an outgoing message all include explicit
 transportDomain and transportAddress parameters.  The values within
 the securityStateReference cache might override these parameters for
 outgoing messages.

5.2.2. securityName

 There are actually three distinct "identities" that can be identified
 during the processing of an SNMP request over a secure transport:
 o  transport principal: the transport-authenticated identity on whose
    behalf the secure transport connection was (or should be)
    established.  This value is transport-, mechanism-, and
    implementation-specific, and is only used within a given Transport
    Model.
 o  tmSecurityName: a human-readable name (in snmpAdminString format)
    representing this transport identity.  This value is transport-
    and implementation-specific, and is only used (directly) by the
    Transport and Security Models.
 o  securityName: a human-readable name (in snmpAdminString format)
    representing the SNMP principal in a model-independent manner.
    This value is used directly by SNMP Applications, the Access
    Control Subsystem, the Message Processing Subsystem, and the
    Security Subsystem.
 The transport principal might or might not be the same as the
 tmSecurityName.  Similarly, the tmSecurityName might or might not be
 the same as the securityName as seen by the Application and Access
 Control Subsystems.  In particular, a non-transport-aware Security
 Model will ignore tmSecurityName completely when determining the SNMP
 securityName.
 However, it is important that the mapping between the transport
 principal and the SNMP securityName (for transport-aware Security
 Models) is consistent and predictable in order to allow configuration
 of suitable access control and the establishment of transport
 connections.

Harrington & Schoenwaelder Standards Track [Page 19] RFC 5590 SNMP Transport Subsystem June 2009

5.2.3. securityLevel

 There are two distinct issues relating to security level as applied
 to secure transports.  For clarity, these are handled by separate
 fields in the tmStateReference cache:
 o  tmTransportSecurityLevel: an indication from the Transport Model
    of the level of security offered by this session.  The Security
    Model can use this to ensure that incoming messages were suitably
    protected before acting on them.
 o  tmRequestedSecurityLevel: an indication from the Security Model of
    the level of security required to be provided by the transport
    protocol.  The Transport Model can use this to ensure that
    outgoing messages will not be sent over an insufficiently secure
    session.

5.2.4. Session Information

 For security reasons, if a secure transport session is closed between
 the time a request message is received and the corresponding response
 message is sent, then the response message SHOULD be discarded, even
 if a new session has been established.  The SNMPv3 WG decided that
 this should be a "SHOULD" architecturally, and it is a Security-
 Model-specific decision whether to REQUIRE this.
 o  tmSameSecurity: this flag is used by a transport-aware Security
    Model to indicate whether the Transport Model MUST enforce this
    restriction.
 o  tmSessionID: in order to verify whether the session has changed,
    the Transport Model must be able to compare the session used to
    receive the original request with the one to be used to send the
    response.  This typically needs some form of session identifier.
    This value is only ever used by the Transport Model, so the format
    and interpretation of this field are model-specific and
    implementation-dependent.
 When processing an outgoing message, if tmSameSecurity is true, then
 the tmSessionID MUST match the current transport session; otherwise,
 the message MUST be discarded and the Dispatcher notified that
 sending the message failed.

Harrington & Schoenwaelder Standards Track [Page 20] RFC 5590 SNMP Transport Subsystem June 2009

6. Abstract Service Interfaces

 Abstract service interfaces have been defined by RFC 3411 to describe
 the conceptual data flows between the various subsystems within an
 SNMP entity and to help keep the subsystems independent of each other
 except for the common parameters.
 This document introduces a couple of new ASIs to define the interface
 between the Transport and Dispatcher Subsystems; it also extends some
 of the ASIs defined in RFC 3411 to include transport-related
 information.
 This document follows the example of RFC 3411 regarding the release
 of state information and regarding error indications.
 1) The release of state information is not always explicitly
 specified in a Transport Model.  As a general rule, if state
 information is available when a message gets discarded, the message-
 state information should also be released, and if state information
 is available when a session is closed, the session-state information
 should also be released.  Keeping sensitive security information
 longer than necessary might introduce potential vulnerabilities to an
 implementation.
 2)An error indication in statusInformation will typically include the
 Object Identifier (OID) and value for an incremented error counter.
 This might be accompanied by values for contextEngineID and
 contextName for this counter, a value for securityLevel, and the
 appropriate state reference if the information is available at the
 point where the error is detected.

6.1. sendMessage ASI

 The sendMessage ASI is used to pass a message from the Dispatcher to
 the appropriate Transport Model for sending.  The sendMessageASI
 defined in this document replaces the text "Send SNMP Request Message
 to Network" that appears in the diagram in Section 4.6.1 of RFC 3411
 and the text "Send SNMP Message to Network" that appears in Section
 4.6.2 of RFC 3411.
 If present and valid, the tmStateReference refers to a cache
 containing Transport-Model-specific parameters for the transport and
 transport security.  How a tmStateReference is determined to be
 present and valid is implementation-dependent.  How the information
 in the cache is used is Transport-Model-dependent and implementation-
 dependent.

Harrington & Schoenwaelder Standards Track [Page 21] RFC 5590 SNMP Transport Subsystem June 2009

 This might sound underspecified, but a Transport Model might be
 something like SNMP over UDP over IPv6, where no security is
 provided, so it might have no mechanisms for utilizing a
 tmStateReference cache.
 statusInformation =
 sendMessage(
 IN   destTransportDomain           -- transport domain to be used
 IN   destTransportAddress          -- transport address to be used
 IN   outgoingMessage               -- the message to send
 IN   outgoingMessageLength         -- its length
 IN   tmStateReference              -- reference to transport state
  )

6.2. Changes to RFC 3411 Outgoing ASIs

 Additional parameters have been added to the ASIs defined in RFC 3411
 that are concerned with communication between the Dispatcher and
 Message Processing Subsystems, and between the Message Processing and
 Security Subsystems.

6.2.1. Message Processing Subsystem Primitives

 A tmStateReference parameter has been added as an OUT parameter to
 the prepareOutgoingMessage and prepareResponseMessage ASIs.  This is
 passed from the Message Processing Subsystem to the Dispatcher, and
 from there to the Transport Subsystem.
 How or if the Message Processing Subsystem modifies or utilizes the
 contents of the cache is Message-Processing-Model specific.
 statusInformation =          -- success or errorIndication
 prepareOutgoingMessage(
 IN  transportDomain          -- transport domain to be used
 IN  transportAddress         -- transport address to be used
 IN  messageProcessingModel   -- typically, SNMP version
 IN  securityModel            -- Security Model to use
 IN  securityName             -- on behalf of this principal
 IN  securityLevel            -- Level of Security requested
 IN  contextEngineID          -- data from/at this entity
 IN  contextName              -- data from/in this context
 IN  pduVersion               -- the version of the PDU
 IN  PDU                      -- SNMP Protocol Data Unit
 IN  expectResponse           -- TRUE or FALSE
 IN  sendPduHandle            -- the handle for matching
                                 incoming responses

Harrington & Schoenwaelder Standards Track [Page 22] RFC 5590 SNMP Transport Subsystem June 2009

 OUT  destTransportDomain     -- destination transport domain
 OUT  destTransportAddress    -- destination transport address
 OUT  outgoingMessage         -- the message to send
 OUT  outgoingMessageLength   -- its length
 OUT  tmStateReference        -- (NEW) reference to transport state
             )
 statusInformation =          -- success or errorIndication
 prepareResponseMessage(
 IN  messageProcessingModel   -- typically, SNMP version
 IN  securityModel            -- Security Model to use
 IN  securityName             -- on behalf of this principal
 IN  securityLevel            -- Level of Security requested
 IN  contextEngineID          -- data from/at this entity
 IN  contextName              -- data from/in this context
 IN  pduVersion               -- the version of the PDU
 IN  PDU                      -- SNMP Protocol Data Unit
 IN  maxSizeResponseScopedPDU -- maximum size able to accept
 IN  stateReference           -- reference to state information
                              -- as presented with the request
 IN  statusInformation        -- success or errorIndication
                              -- error counter OID/value if error
 OUT destTransportDomain      -- destination transport domain
 OUT destTransportAddress     -- destination transport address
 OUT outgoingMessage          -- the message to send
 OUT outgoingMessageLength    -- its length
 OUT tmStateReference         -- (NEW) reference to transport state
             )

6.2.2. Security Subsystem Primitives

 transportDomain and transportAddress parameters have been added as IN
 parameters to the generateRequestMsg and generateResponseMsg ASIs,
 and a tmStateReference parameter has been added as an OUT parameter.
 The transportDomain and transportAddress parameters will have been
 passed into the Message Processing Subsystem from the Dispatcher and
 are passed on to the Security Subsystem.  The tmStateReference
 parameter will be passed from the Security Subsystem back to the
 Message Processing Subsystem, and on to the Dispatcher and Transport
 Subsystems.
 If a cache exists for a session identifiable from the
 tmTransportDomain, tmTransportAddress, tmSecurityName, and requested
 securityLevel, then a transport-aware Security Model might create a
 tmStateReference parameter to this cache and pass that as an OUT
 parameter.

Harrington & Schoenwaelder Standards Track [Page 23] RFC 5590 SNMP Transport Subsystem June 2009

 statusInformation =
 generateRequestMsg(
   IN   transportDomain         -- (NEW) destination transport domain
   IN   transportAddress        -- (NEW) destination transport address
   IN   messageProcessingModel  -- typically, SNMP version
   IN   globalData              -- message header, admin data
   IN   maxMessageSize          -- of the sending SNMP entity
   IN   securityModel           -- for the outgoing message
   IN   securityEngineID        -- authoritative SNMP entity
   IN   securityName            -- on behalf of this principal
   IN   securityLevel           -- Level of Security requested
   IN   scopedPDU               -- message (plaintext) payload
   OUT  securityParameters      -- filled in by Security Module
   OUT  wholeMsg                -- complete generated message
   OUT  wholeMsgLength          -- length of generated message
   OUT  tmStateReference        -- (NEW) reference to transport state
            )
 statusInformation =
 generateResponseMsg(
   IN   transportDomain         -- (NEW) destination transport domain
   IN   transportAddress        -- (NEW) destination transport address
   IN   messageProcessingModel -- Message Processing Model
   IN   globalData             -- msgGlobalData
   IN   maxMessageSize         -- from msgMaxSize
   IN   securityModel          -- as determined by MPM
   IN   securityEngineID       -- the value of snmpEngineID
   IN   securityName           -- on behalf of this principal
   IN   securityLevel          -- for the outgoing message
   IN   scopedPDU              -- as provided by MPM
   IN   securityStateReference -- as provided by MPM
   OUT  securityParameters     -- filled in by Security Module
   OUT  wholeMsg               -- complete generated message
   OUT  wholeMsgLength         -- length of generated message
   OUT  tmStateReference       -- (NEW) reference to transport state
            )

6.3. The receiveMessage ASI

 The receiveMessage ASI is used to pass a message from the Transport
 Subsystem to the Dispatcher.  The receiveMessage ASI replaces the
 text "Receive SNMP Response Message from Network" that appears in the
 diagram in Section 4.6.1 of RFC 3411 and the text "Receive SNMP
 Message from Network" from Section 4.6.2 of RFC3411.
 When a message is received on a given transport session, if a cache
 does not already exist for that session, the Transport Model might
 create one, referenced by tmStateReference.  The contents of this

Harrington & Schoenwaelder Standards Track [Page 24] RFC 5590 SNMP Transport Subsystem June 2009

 cache are discussed in Section 5.  How this information is determined
 is implementation- and Transport-Model-specific.
 "Might create one" might sound underspecified, but a Transport Model
 might be something like SNMP over UDP over IPv6, where transport
 security is not provided, so it might not create a cache.
 The Transport Model does not know the securityModel for an incoming
 message; this will be determined by the Message Processing Model in a
 Message-Processing-Model-dependent manner.
 statusInformation =
 receiveMessage(
 IN   transportDomain               -- origin transport domain
 IN   transportAddress              -- origin transport address
 IN   incomingMessage               -- the message received
 IN   incomingMessageLength         -- its length
 IN   tmStateReference              -- reference to transport state
  )

6.4. Changes to RFC 3411 Incoming ASIs

 The tmStateReference parameter has also been added to some of the
 incoming ASIs defined in RFC 3411.  How or if a Message Processing
 Model or Security Model uses tmStateReference is message-processing-
 and Security-Model-specific.
 This might sound underspecified, but a Message Processing Model might
 have access to all the information from the cache and from the
 message.  The Message Processing Model might determine that the USM
 Security Model is specified in an SNMPv3 message header; the USM
 Security Model has no need of values in the tmStateReference cache to
 authenticate and secure the SNMP message, but an Application might
 have specified to use a secure transport such as that provided by the
 SSH Transport Model to send the message to its destination.

6.4.1. Message Processing Subsystem Primitive

 The tmStateReference parameter of prepareDataElements is passed from
 the Dispatcher to the Message Processing Subsystem.  How or if the
 Message Processing Subsystem modifies or utilizes the contents of the
 cache is Message-Processing-Model-specific.
 result =                       -- SUCCESS or errorIndication
 prepareDataElements(
 IN   transportDomain           -- origin transport domain
 IN   transportAddress          -- origin transport address
 IN   wholeMsg                  -- as received from the network

Harrington & Schoenwaelder Standards Track [Page 25] RFC 5590 SNMP Transport Subsystem June 2009

 IN   wholeMsgLength            -- as received from the network
 IN   tmStateReference          -- (NEW) from the Transport Model
 OUT  messageProcessingModel    -- typically, SNMP version
 OUT  securityModel             -- Security Model to use
 OUT  securityName              -- on behalf of this principal
 OUT  securityLevel             -- Level of Security requested
 OUT  contextEngineID           -- data from/at this entity
 OUT  contextName               -- data from/in this context
 OUT  pduVersion                -- the version of the PDU
 OUT  PDU                       -- SNMP Protocol Data Unit
 OUT  pduType                   -- SNMP PDU type
 OUT  sendPduHandle             -- handle for matched request
 OUT  maxSizeResponseScopedPDU  -- maximum size sender can accept
 OUT  statusInformation         -- success or errorIndication
                                -- error counter OID/value if error
 OUT  stateReference            -- reference to state information
                                -- to be used for possible Response
 )

6.4.2. Security Subsystem Primitive

 The processIncomingMessage ASI passes tmStateReference from the
 Message Processing Subsystem to the Security Subsystem.
 If tmStateReference is present and valid, an appropriate Security
 Model might utilize the information in the cache.  How or if the
 Security Subsystem utilizes the information in the cache is Security-
 Model-specific.
 statusInformation =  -- errorIndication or success
                          -- error counter OID/value if error
 processIncomingMsg(
 IN   messageProcessingModel    -- typically, SNMP version
 IN   maxMessageSize            -- of the sending SNMP entity
 IN   securityParameters        -- for the received message
 IN   securityModel             -- for the received message
 IN   securityLevel             -- Level of Security
 IN   wholeMsg                  -- as received on the wire
 IN   wholeMsgLength            -- length as received on the wire
 IN   tmStateReference          -- (NEW) from the Transport Model
 OUT  securityEngineID          -- authoritative SNMP entity
 OUT  securityName              -- identification of the principal
 OUT  scopedPDU,                -- message (plaintext) payload
 OUT  maxSizeResponseScopedPDU  -- maximum size sender can handle
 OUT  securityStateReference    -- reference to security state
                                -- information, needed for response
 )

Harrington & Schoenwaelder Standards Track [Page 26] RFC 5590 SNMP Transport Subsystem June 2009

7. Security Considerations

 This document defines an architectural approach that permits SNMP to
 utilize transport-layer security services.  Each proposed Transport
 Model should discuss the security considerations of that Transport
 Model.
 It is considered desirable by some industry segments that SNMP
 Transport Models utilize transport-layer security that addresses
 perfect forward secrecy at least for encryption keys.  Perfect
 forward secrecy guarantees that compromise of long-term secret keys
 does not result in disclosure of past session keys.  Each proposed
 Transport Model should include a discussion in its security
 considerations of whether perfect forward secrecy is appropriate for
 that Transport Model.
 The denial-of-service characteristics of various Transport Models and
 security protocols will vary and should be evaluated when determining
 the applicability of a Transport Model to a particular deployment
 situation.
 Since the cache will contain security-related parameters,
 implementers SHOULD store this information (in memory or in
 persistent storage) in a manner to protect it from unauthorized
 disclosure and/or modification.
 Care must be taken to ensure that an SNMP engine is sending packets
 out over a transport using credentials that are legal for that engine
 to use on behalf of that user.  Otherwise, an engine that has
 multiple transports open might be "tricked" into sending a message
 through the wrong transport.
 A Security Model might have multiple sources from which to define the
 securityName and securityLevel.  The use of a secure Transport Model
 does not imply that the securityName and securityLevel chosen by the
 Security Model represent the transport-authenticated identity or the
 transport-provided security services.  The securityModel,
 securityName, and securityLevel parameters are a related set, and an
 administrator should understand how the specified securityModel
 selects the corresponding securityName and securityLevel.

7.1. Coexistence, Security Parameters, and Access Control

 In the RFC 3411 architecture, the Message Processing Model makes the
 decision about which Security Model to use.  The architectural change
 described by this document does not alter that.

Harrington & Schoenwaelder Standards Track [Page 27] RFC 5590 SNMP Transport Subsystem June 2009

 The architecture change described by this document does, however,
 allow SNMP to support two different approaches to security --
 message-driven security and transport-driven security.  With message-
 driven security, SNMP provides its own security and passes security
 parameters within the SNMP message; with transport-driven security,
 SNMP depends on an external entity to provide security during
 transport by "wrapping" the SNMP message.
 Using a non-transport-aware Security Model with a secure Transport
 Model is NOT RECOMMENDED for the following reasons.
 Security Models defined before the Transport Security Model (i.e.,
 SNMPv1, SNMPv2c, and USM) do not support transport-based security and
 only have access to the security parameters contained within the SNMP
 message.  They do not know about the security parameters associated
 with a secure transport.  As a result, the Access Control Subsystem
 bases its decisions on the security parameters extracted from the
 SNMP message, not on transport-based security parameters.
 Implications of combining older Security Models with Secure Transport
 Models are known.  The securityName used for access control decisions
 is based on the message-driven identity, which might be
 unauthenticated, and not on the transport-driven, authenticated
 identity:
 o  An SNMPv1 message will always be paired with an SNMPv1 Security
    Model (per RFC 3584), regardless of the transport mapping or
    Transport Model used, and access controls will be based on the
    unauthenticated community name.
 o  An SNMPv2c message will always be paired with an SNMPv2c Security
    Model (per RFC 3584), regardless of the transport mapping or
    Transport Model used, and access controls will be based on the
    unauthenticated community name.
 o  An SNMPv3 message will always be paired with the securityModel
    specified in the msgSecurityParameters field of the message (per
    RFC 3412), regardless of the transport mapping or Transport Model
    used.  If the SNMPv3 message specifies the User-based Security
    Model (USM) with noAuthNoPriv, then the access controls will be
    based on the unauthenticated USM user.
 o  For outgoing messages, if a Secure Transport Model is selected in
    combination with a Security Model that does not populate a
    tmStateReference, the Secure Transport Model SHOULD detect the
    lack of a valid tmStateReference and fail.

Harrington & Schoenwaelder Standards Track [Page 28] RFC 5590 SNMP Transport Subsystem June 2009

 In times of network stress, a Secure Transport Model might not work
 properly if its underlying security mechanisms (e.g., Network Time
 Protocol (NTP) or Authentication, Authorization, and Accounting (AAA)
 protocols or certificate authorities) are not reachable.  The User-
 based Security Model was explicitly designed to not depend upon
 external network services, and provides its own security services.
 It is RECOMMENDED that operators provision authPriv USM as a fallback
 mechanism to supplement any Security Model or Transport Model that
 has external dependencies, so that secure SNMP communications can
 continue when the external network service is not available.

8. IANA Considerations

 IANA has created a new registry in the Simple Network Management
 Protocol (SNMP) Number Spaces.  The new registry is called "SNMP
 Transport Domains".  This registry contains US-ASCII alpha-numeric
 strings of one to four characters to identify prefixes for
 corresponding SNMP transport domains.  Each transport domain MUST
 have an OID assignment under snmpDomains [RFC2578].  Values are to be
 assigned via [RFC5226] "Specification Required".
 The registry has been populated with the following initial entries:
 Registry Name: SNMP Transport Domains
 Reference: [RFC2578] [RFC3417] [RFC5590]
 Registration Procedures: Specification Required
 Each domain is assigned a MIB-defined OID under snmpDomains
 Prefix        snmpDomains                    Reference
 -------       -----------------------------  ---------
 udp           snmpUDPDomain                  [RFC3417] [RFC5590]
 clns          snmpCLNSDomain                 [RFC3417] [RFC5590]
 cons          snmpCONSDomain                 [RFC3417] [RFC5590]
 ddp           snmpDDPDomain                  [RFC3417] [RFC5590]
 ipx           snmpIPXDomain                  [RFC3417] [RFC5590]
 prxy          rfc1157Domain                  [RFC3417] [RFC5590]

9. Acknowledgments

 The Integrated Security for SNMP WG would like to thank the following
 people for their contributions to the process.
 The authors of submitted Security Model proposals: Chris Elliot, Wes
 Hardaker, David Harrington, Keith McCloghrie, Kaushik Narayan, David
 Perkins, Joseph Salowey, and Juergen Schoenwaelder.
 The members of the Protocol Evaluation Team: Uri Blumenthal,
 Lakshminath Dondeti, Randy Presuhn, and Eric Rescorla.

Harrington & Schoenwaelder Standards Track [Page 29] RFC 5590 SNMP Transport Subsystem June 2009

 WG members who performed detailed reviews: Wes Hardaker, Jeffrey
 Hutzelman, Tom Petch, Dave Shield, and Bert Wijnen.

10. References

10.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC2578]  McCloghrie, K., Ed., Perkins, D., Ed., and J.
            Schoenwaelder, Ed., "Structure of Management Information
            Version 2 (SMIv2)", STD 58, RFC 2578, April 1999.
 [RFC3411]  Harrington, D., Presuhn, R., and B. Wijnen, "An
            Architecture for Describing Simple Network Management
            Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
            December 2002.
 [RFC3412]  Case, J., Harrington, D., Presuhn, R., and B. Wijnen,
            "Message Processing and Dispatching for the Simple Network
            Management Protocol (SNMP)", STD 62, RFC 3412,
            December 2002.
 [RFC3413]  Levi, D., Meyer, P., and B. Stewart, "Simple Network
            Management Protocol (SNMP) Applications", STD 62,
            RFC 3413, December 2002.
 [RFC3414]  Blumenthal, U. and B. Wijnen, "User-based Security Model
            (USM) for version 3 of the Simple Network Management
            Protocol (SNMPv3)", STD 62, RFC 3414, December 2002.
 [RFC3417]  Presuhn, R., "Transport Mappings for the Simple Network
            Management Protocol (SNMP)", STD 62, RFC 3417,
            December 2002.

10.2. Informative References

 [RFC2865]  Rigney, C., Willens, S., Rubens, A., and W. Simpson,
            "Remote Authentication Dial In User Service (RADIUS)",
            RFC 2865, June 2000.
 [RFC3410]  Case, J., Mundy, R., Partain, D., and B. Stewart,
            "Introduction and Applicability Statements for Internet-
            Standard Management Framework", RFC 3410, December 2002.

Harrington & Schoenwaelder Standards Track [Page 30] RFC 5590 SNMP Transport Subsystem June 2009

 [RFC3584]  Frye, R., Levi, D., Routhier, S., and B. Wijnen,
            "Coexistence between Version 1, Version 2, and Version 3
            of the Internet-standard Network Management Framework",
            BCP 74, RFC 3584, August 2003.
 [RFC4251]  Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
            Protocol Architecture", RFC 4251, January 2006.
 [RFC4422]  Melnikov, A. and K. Zeilenga, "Simple Authentication and
            Security Layer (SASL)", RFC 4422, June 2006.
 [RFC4741]  Enns, R., "NETCONF Configuration Protocol", RFC 4741,
            December 2006.
 [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
            IANA Considerations Section in RFCs", BCP 26, RFC 5226,
            May 2008.
 [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
            (TLS) Protocol Version 1.2", RFC 5246, August 2008.
 [RFC5424]  Gerhards, R., "The Syslog Protocol", RFC 5424, March 2009.
 [RFC5591]  Harrington, D. and W. Hardaker, "Transport Security Model
            for the Simple Network Management Protocol (SNMP)",
            RFC 5591, June 2009.
 [RFC5592]  Harrington, D., Salowey, J., and W. Hardaker, "Secure
            Shell Transport Model for the Simple Network Management
            Protocol (SNMP)", RFC 5592, June 2009.

Harrington & Schoenwaelder Standards Track [Page 31] RFC 5590 SNMP Transport Subsystem June 2009

Appendix A. Why tmStateReference?

 This appendix considers why a cache-based approach was selected for
 passing parameters.
 There are four approaches that could be used for passing information
 between the Transport Model and a Security Model.
 1.  One could define an ASI to supplement the existing ASIs.
 2.  One could add a header to encapsulate the SNMP message.
 3.  One could utilize fields already defined in the existing SNMPv3
     message.
 4.  One could pass the information in an implementation-specific
     cache or via a MIB module.

A.1. Define an Abstract Service Interface

 Abstract Service Interfaces (ASIs) are defined by a set of primitives
 that specify the services provided and the abstract data elements
 that are to be passed when the services are invoked.  Defining
 additional ASIs to pass the security and transport information from
 the Transport Subsystem to the Security Subsystem has the advantage
 of being consistent with existing RFC 3411/3412 practice; it also
 helps to ensure that any Transport Model proposals pass the necessary
 data and do not cause side effects by creating model-specific
 dependencies between itself and models or subsystems other than those
 that are clearly defined by an ASI.

A.2. Using an Encapsulating Header

 A header could encapsulate the SNMP message to pass necessary
 information from the Transport Model to the Dispatcher and then to a
 Message Processing Model.  The message header would be included in
 the wholeMessage ASI parameter and would be removed by a
 corresponding Message Processing Model.  This would imply the (one
 and only) Message Dispatcher would need to be modified to determine
 which SNMP message version was involved, and a new Message Processing
 Model would need to be developed that knew how to extract the header
 from the message and pass it to the Security Model.

A.3. Modifying Existing Fields in an SNMP Message

 [RFC3412] defines the SNMPv3 message, which contains fields to pass
 security-related parameters.  The Transport Subsystem could use these
 fields in an SNMPv3 message (or comparable fields in other message

Harrington & Schoenwaelder Standards Track [Page 32] RFC 5590 SNMP Transport Subsystem June 2009

 formats) to pass information between Transport Models in different
 SNMP engines and to pass information between a Transport Model and a
 corresponding Message Processing Model.
 If the fields in an incoming SNMPv3 message are changed by the
 Transport Model before passing it to the Security Model, then the
 Transport Model will need to decode the ASN.1 message, modify the
 fields, and re-encode the message in ASN.1 before passing the message
 on to the Message Dispatcher or to the transport layer.  This would
 require an intimate knowledge of the message format and message
 versions in order for the Transport Model to know which fields could
 be modified.  This would seriously violate the modularity of the
 architecture.

A.4. Using a Cache

 This document describes a cache into which the Transport Model (TM)
 puts information about the security applied to an incoming message; a
 Security Model can extract that information from the cache.  Given
 that there might be multiple TM security caches, a tmStateReference
 is passed as an extra parameter in the ASIs between the Transport
 Subsystem and the Security Subsystem so that the Security Model knows
 which cache of information to consult.
 This approach does create dependencies between a specific Transport
 Model and a corresponding specific Security Model.  However, the
 approach of passing a model-independent reference to a model-
 dependent cache is consistent with the securityStateReference already
 being passed around in the RFC 3411 ASIs.

Harrington & Schoenwaelder Standards Track [Page 33] RFC 5590 SNMP Transport Subsystem June 2009

Authors' Addresses

 David Harrington
 Huawei Technologies (USA)
 1700 Alma Dr. Suite 100
 Plano, TX 75075
 USA
 Phone: +1 603 436 8634
 EMail: ietfdbh@comcast.net
 Juergen Schoenwaelder
 Jacobs University Bremen
 Campus Ring 1
 28725 Bremen
 Germany
 Phone: +49 421 200-3587
 EMail: j.schoenwaelder@jacobs-university.de

Harrington & Schoenwaelder Standards Track [Page 34]

Network Working Group D. Harrington Request for Comments: 5591 Huawei Technologies (USA) Category: Standards Track W. Hardaker

                                             Cobham Analytic Solutions
                                                             June 2009
                  Transport Security Model for the
             Simple Network Management Protocol (SNMP)

Status of This Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

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 document authors.  All rights reserved.
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 Provisions Relating to IETF Documents in effect on the date of
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 Contributions published or made publicly available before November
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Harrington & Hardaker Standards Track [Page 1] RFC 5591 Transport Security Model for SNMP June 2009

Abstract

 This memo describes a Transport Security Model for the Simple Network
 Management Protocol (SNMP).
 This memo also defines a portion of the Management Information Base
 (MIB) for monitoring and managing the Transport Security Model for
 SNMP.

Table of Contents

 1. Introduction ....................................................3
    1.1. The Internet-Standard Management Framework .................3
    1.2. Conventions ................................................3
    1.3. Modularity .................................................4
    1.4. Motivation .................................................5
    1.5. Constraints ................................................5
 2. How the Transport Security Model Fits in the Architecture .......6
    2.1. Security Capabilities of this Model ........................6
         2.1.1. Threats .............................................6
         2.1.2. Security Levels .....................................7
    2.2. Transport Sessions .........................................7
    2.3. Coexistence ................................................7
         2.3.1. Coexistence with Message Processing Models ..........7
         2.3.2. Coexistence with Other Security Models ..............8
         2.3.3. Coexistence with Transport Models ...................8
 3. Cached Information and References ...............................8
    3.1. Transport Security Model Cached Information ................9
         3.1.1. securityStateReference ..............................9
         3.1.2. tmStateReference ....................................9
         3.1.3. Prefixes and securityNames ..........................9
 4. Processing an Outgoing Message .................................10
    4.1. Security Processing for an Outgoing Message ...............10
    4.2. Elements of Procedure for Outgoing Messages ...............11
 5. Processing an Incoming SNMP Message ............................12
    5.1. Security Processing for an Incoming Message ...............12
    5.2. Elements of Procedure for Incoming Messages ...............13
 6. MIB Module Overview ............................................14
    6.1. Structure of the MIB Module ...............................14
         6.1.1. The snmpTsmStats Subtree ...........................14
         6.1.2. The snmpTsmConfiguration Subtree ...................14
    6.2. Relationship to Other MIB Modules .........................14
         6.2.1. MIB Modules Required for IMPORTS ...................15
 7. MIB Module Definition ..........................................15
 8. Security Considerations ........................................20
    8.1. MIB Module Security .......................................20
 9. IANA Considerations ............................................21
 10. Acknowledgments ...............................................22

Harrington & Hardaker Standards Track [Page 2] RFC 5591 Transport Security Model for SNMP June 2009

 11. References ....................................................22
    11.1. Normative References .....................................22
    11.2. Informative References ...................................23
 Appendix A.  Notification Tables Configuration ....................24
   A.1.  Transport Security Model Processing for Notifications .....25
 Appendix B.  Processing Differences between USM and Secure
              Transport ............................................26
   B.1.  USM and the RFC 3411 Architecture .........................26
   B.2.  Transport Subsystem and the RFC 3411 Architecture .........27

1. Introduction

 This memo describes a Transport Security Model for the Simple Network
 Management Protocol for use with secure Transport Models in the
 Transport Subsystem [RFC5590].
 This memo also defines a portion of the Management Information Base
 (MIB) for monitoring and managing the Transport Security Model for
 SNMP.
 It is important to understand the SNMP architecture and the
 terminology of the architecture to understand where the Transport
 Security Model described in this memo fits into the architecture and
 interacts with other subsystems and models within the architecture.
 It is expected that readers will have also read and understood
 [RFC3411], [RFC3412], [RFC3413], and [RFC3418].

1.1. The Internet-Standard Management Framework

 For a detailed overview of the documents that describe the current
 Internet-Standard Management Framework, please refer to section 7 of
 RFC 3410 [RFC3410].
 Managed objects are accessed via a virtual information store, termed
 the Management Information Base or MIB.  MIB objects are generally
 accessed through the Simple Network Management Protocol (SNMP).
 Objects in the MIB are defined using the mechanisms defined in the
 Structure of Management Information (SMI).  This memo specifies a MIB
 module that is compliant to the SMIv2, which is described in STD 58,
 RFC 2578 [RFC2578], STD 58, RFC 2579 [RFC2579] and STD 58, RFC 2580
 [RFC2580].

1.2. Conventions

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in [RFC2119].

Harrington & Hardaker Standards Track [Page 3] RFC 5591 Transport Security Model for SNMP June 2009

 Lowercase versions of the keywords should be read as in normal
 English.  They will usually, but not always, be used in a context
 that relates to compatibility with the RFC 3411 architecture or the
 subsystem defined here but that might have no impact on on-the-wire
 compatibility.  These terms are used as guidance for designers of
 proposed IETF models to make the designs compatible with RFC 3411
 subsystems and Abstract Service Interfaces (ASIs).  Implementers are
 free to implement differently.  Some usages of these lowercase terms
 are simply normal English usage.
 For consistency with SNMP-related specifications, this document
 favors terminology as defined in STD 62, rather than favoring
 terminology that is consistent with non-SNMP specifications that use
 different variations of the same terminology.  This is consistent
 with the IESG decision to not require the SNMPv3 terminology be
 modified to match the usage of other non-SNMP specifications when
 SNMPv3 was advanced to Full Standard.
 Authentication in this document typically refers to the English
 meaning of "serving to prove the authenticity of" the message, not
 data source authentication or peer identity authentication.
 The terms "manager" and "agent" are not used in this document
 because, in the RFC 3411 architecture, all SNMP entities have the
 capability of acting as manager, agent, or both depending on the SNMP
 applications included in the engine.  Where distinction is needed,
 the application names of command generator, command responder,
 notification originator, notification receiver, and proxy forwarder
 are used.  See "Simple Network Management Protocol (SNMP)
 Applications" [RFC3413] for further information.
 While security protocols frequently refer to a user, the terminology
 used in [RFC3411] and in this memo is "principal".  A principal is
 the "who" on whose behalf services are provided or processing takes
 place.  A principal can be, among other things, an individual acting
 in a particular role, a set of individuals each acting in a
 particular role, an application or a set of applications, or a
 combination of these within an administrative domain.

1.3. Modularity

 The reader is expected to have read and understood the description of
 the SNMP architecture, as defined in [RFC3411], and the architecture
 extension specified in "Transport Subsystem for the Simple Network
 Management Protocol (SNMP)" [RFC5590], which enables the use of
 external "lower-layer transport" protocols to provide message

Harrington & Hardaker Standards Track [Page 4] RFC 5591 Transport Security Model for SNMP June 2009

 security.  Transport Models are tied into the SNMP architecture
 through the Transport Subsystem.  The Transport Security Model is
 designed to work with such lower-layer, secure Transport Models.
 In keeping with the RFC 3411 design decisions to use self-contained
 documents, this memo includes the elements of procedure plus
 associated MIB objects that are needed for processing the Transport
 Security Model for SNMP.  These MIB objects SHOULD NOT be referenced
 in other documents.  This allows the Transport Security Model to be
 designed and documented as independent and self-contained, having no
 direct impact on other modules.  It also allows this module to be
 upgraded and supplemented as the need arises, and to move along the
 standards track on different time-lines from other modules.
 This modularity of specification is not meant to be interpreted as
 imposing any specific requirements on implementation.

1.4. Motivation

 This memo describes a Security Model to make use of Transport Models
 that use lower-layer, secure transports and existing and commonly
 deployed security infrastructures.  This Security Model is designed
 to meet the security and operational needs of network administrators,
 maximize usability in operational environments to achieve high
 deployment success, and at the same time minimize implementation and
 deployment costs to minimize the time until deployment is possible.

1.5. Constraints

 The design of this SNMP Security Model is also influenced by the
 following constraints:
 1.  In times of network stress, the security protocol and its
     underlying security mechanisms SHOULD NOT depend solely upon the
     ready availability of other network services (e.g., Network Time
     Protocol (NTP) or Authentication, Authorization, and Accounting
     (AAA) protocols).
 2.  When the network is not under stress, the Security Model and its
     underlying security mechanisms MAY depend upon the ready
     availability of other network services.
 3.  It might not be possible for the Security Model to determine when
     the network is under stress.
 4.  A Security Model SHOULD NOT require changes to the SNMP
     architecture.

Harrington & Hardaker Standards Track [Page 5] RFC 5591 Transport Security Model for SNMP June 2009

 5.  A Security Model SHOULD NOT require changes to the underlying
     security protocol.

2. How the Transport Security Model Fits in the Architecture

 The Transport Security Model is designed to fit into the RFC 3411
 architecture as a Security Model in the Security Subsystem and to
 utilize the services of a secure Transport Model.
 For incoming messages, a secure Transport Model will pass a
 tmStateReference cache, described in [RFC5590].  To maintain RFC 3411
 modularity, the Transport Model will not know which securityModel
 will process the incoming message; the Message Processing Model will
 determine this.  If the Transport Security Model is used with a non-
 secure Transport Model, then the cache will not exist or will not be
 populated with security parameters, which will cause the Transport
 Security Model to return an error (see Section 5.2).
 The Transport Security Model will create the securityName and
 securityLevel to be passed to applications, and will verify that the
 tmTransportSecurityLevel reported by the Transport Model is at least
 as strong as the securityLevel requested by the Message Processing
 Model.
 For outgoing messages, the Transport Security Model will create a
 tmStateReference cache (or use an existing one), and will pass the
 tmStateReference to the specified Transport Model.

2.1. Security Capabilities of this Model

2.1.1. Threats

 The Transport Security Model is compatible with the RFC 3411
 architecture and provides protection against the threats identified
 by the RFC 3411 architecture.  However, the Transport Security Model
 does not provide security mechanisms such as authentication and
 encryption itself.  Which threats are addressed and how they are
 mitigated depends on the Transport Model used.  To avoid creating
 potential security vulnerabilities, operators should configure their
 system so this Security Model is always used with a Transport Model
 that provides appropriate security, where "appropriate" for a
 particular deployment is an administrative decision.

Harrington & Hardaker Standards Track [Page 6] RFC 5591 Transport Security Model for SNMP June 2009

2.1.2. Security Levels

 The RFC 3411 architecture recognizes three levels of security:
  1. without authentication and without privacy (noAuthNoPriv)
  1. with authentication but without privacy (authNoPriv)
  1. with authentication and with privacy (authPriv)
 The model-independent securityLevel parameter is used to request
 specific levels of security for outgoing messages and to assert that
 specific levels of security were applied during the transport and
 processing of incoming messages.
 The transport-layer algorithms used to provide security should not be
 exposed to the Transport Security Model, as the Transport Security
 Model has no mechanisms by which it can test whether an assertion
 made by a Transport Model is accurate.
 The Transport Security Model trusts that the underlying secure
 transport connection has been properly configured to support security
 characteristics at least as strong as reported in
 tmTransportSecurityLevel.

2.2. Transport Sessions

 The Transport Security Model does not work with transport sessions
 directly.  Instead the transport-related state is associated with a
 unique combination of transportDomain, transportAddress,
 securityName, and securityLevel, and is referenced via the
 tmStateReference parameter.  How and if this is mapped to a
 particular transport or channel is the responsibility of the
 Transport Subsystem.

2.3. Coexistence

 In the RFC 3411 architecture, a Message Processing Model determines
 which Security Model SHALL be called.  As of this writing, IANA has
 registered four Message Processing Models (SNMPv1, SNMPv2c, SNMPv2u/
 SNMPv2*, and SNMPv3) and three other Security Models (SNMPv1,
 SNMPv2c, and the User-based Security Model).

2.3.1. Coexistence with Message Processing Models

 The SNMPv1 and SNMPv2c message processing described in BCP 74
 [RFC3584] always selects the SNMPv1(1) and SNMPv2c(2) Security
 Models.  Since there is no mechanism defined in RFC 3584 to select an

Harrington & Hardaker Standards Track [Page 7] RFC 5591 Transport Security Model for SNMP June 2009

 alternative Security Model, SNMPv1 and SNMPv2c messages cannot use
 the Transport Security Model.  Messages might still be able to be
 conveyed over a secure transport protocol, but the Transport Security
 Model will not be invoked.
 The SNMPv2u/SNMPv2* Message Processing Model is an historic artifact
 for which there is no existing IETF specification.
 The SNMPv3 message processing defined in [RFC3412] extracts the
 securityModel from the msgSecurityModel field of an incoming
 SNMPv3Message.  When this value is transportSecurityModel(4),
 security processing is directed to the Transport Security Model.  For
 an outgoing message to be secured using the Transport Security Model,
 the application MUST specify a securityModel parameter value of
 transportSecurityModel(4) in the sendPdu Abstract Service Interface
 (ASI).

2.3.2. Coexistence with Other Security Models

 The Transport Security Model uses its own MIB module for processing
 to maintain independence from other Security Models.  This allows the
 Transport Security Model to coexist with other Security Models, such
 as the User-based Security Model (USM) [RFC3414].

2.3.3. Coexistence with Transport Models

 The Transport Security Model (TSM) MAY work with multiple Transport
 Models, but the RFC 3411 Abstract Service Interfaces (ASIs) do not
 carry a value for the Transport Model.  The MIB module defined in
 this memo allows an administrator to configure whether or not TSM
 prepends a Transport Model prefix to the securityName.  This will
 allow SNMP applications to consider Transport Model as a factor when
 making decisions, such as access control, notification generation,
 and proxy forwarding.
 To have SNMP properly utilize the security services coordinated by
 the Transport Security Model, this Security Model MUST only be used
 with Transport Models that know how to process a tmStateReference,
 such as the Secure Shell Transport Model [RFC5592].

3. Cached Information and References

 When performing SNMP processing, there are two levels of state
 information that might need to be retained: the immediate state
 linking a request-response pair and a potentially longer-term state
 relating to transport and security.  "Transport Subsystem for the
 Simple Network Management Protocol (SNMP)" [RFC5590] defines general
 requirements for caches and references.

Harrington & Hardaker Standards Track [Page 8] RFC 5591 Transport Security Model for SNMP June 2009

 This document defines additional cache requirements related to the
 Transport Security Model.

3.1. Transport Security Model Cached Information

 The Transport Security Model has specific responsibilities regarding
 the cached information.

3.1.1. securityStateReference

 The Transport Security Model adds the tmStateReference received from
 the processIncomingMsg ASI to the securityStateReference.  This
 tmStateReference can then be retrieved during the generateResponseMsg
 ASI so that it can be passed back to the Transport Model.

3.1.2. tmStateReference

 For outgoing messages, the Transport Security Model uses parameters
 provided by the SNMP application to look up or create a
 tmStateReference.
 For the Transport Security Model, the security parameters used for a
 response MUST be the same as those used for the corresponding
 request.  This Security Model uses the tmStateReference stored as
 part of the securityStateReference when appropriate.  For responses
 and reports, this Security Model sets the tmSameSecurity flag to true
 in the tmStateReference before passing it to a Transport Model.
 For incoming messages, the Transport Security Model uses parameters
 provided in the tmStateReference cache to establish a securityName,
 and to verify adequate security levels.

3.1.3. Prefixes and securityNames

 The SNMP-VIEW-BASED-ACM-MIB module [RFC3415], the SNMP-TARGET-MIB
 module [RFC3413], and other MIB modules contain objects to configure
 security parameters for use by applications such as access control,
 notification generation, and proxy forwarding.
 Transport domains and their corresponding prefixes are coordinated
 via the IANA registry "SNMP Transport Domains".
 If snmpTsmConfigurationUsePrefix is set to true, then all
 securityNames provided by, or provided to, the Transport Security
 Model MUST include a valid transport domain prefix.

Harrington & Hardaker Standards Track [Page 9] RFC 5591 Transport Security Model for SNMP June 2009

 If snmpTsmConfigurationUsePrefix is set to false, then all
 securityNames provided by, or provided to, the Transport Security
 Model MUST NOT include a transport domain prefix.
 The tmSecurityName in the tmStateReference stored as part of the
 securityStateReference does not contain a prefix.

4. Processing an Outgoing Message

 An error indication might return an Object Identifier (OID) and value
 for an incremented counter, a value for securityLevel, values for
 contextEngineID and contextName for the counter, and the
 securityStateReference, if this information is available at the point
 where the error is detected.

4.1. Security Processing for an Outgoing Message

 This section describes the procedure followed by the Transport
 Security Model.
 The parameters needed for generating a message are supplied to the
 Security Model by the Message Processing Model via the
 generateRequestMsg() or the generateResponseMsg() ASI.  The Transport
 Subsystem architectural extension has added the transportDomain,
 transportAddress, and tmStateReference parameters to the original RFC
 3411 ASIs.
  statusInformation =                -- success or errorIndication
        generateRequestMsg(
        IN   messageProcessingModel  -- typically, SNMP version
        IN   globalData              -- message header, admin data
        IN   maxMessageSize          -- of the sending SNMP entity
        IN   transportDomain         -- (NEW) specified by application
        IN   transportAddress        -- (NEW) specified by application
        IN   securityModel           -- for the outgoing message
        IN   securityEngineID        -- authoritative SNMP entity
        IN   securityName            -- on behalf of this principal
        IN   securityLevel           -- Level of Security requested
        IN   scopedPDU               -- message (plaintext) payload
        OUT  securityParameters      -- filled in by Security Module
        OUT  wholeMsg                -- complete generated message
        OUT  wholeMsgLength          -- length of generated message
        OUT  tmStateReference        -- (NEW) transport info
             )
statusInformation = -- success or errorIndication
        generateResponseMsg(
        IN   messageProcessingModel  -- typically, SNMP version

Harrington & Hardaker Standards Track [Page 10] RFC 5591 Transport Security Model for SNMP June 2009

        IN   globalData              -- message header, admin data
        IN   maxMessageSize          -- of the sending SNMP entity
        IN   transportDomain         -- (NEW) specified by application
        IN   transportAddress        -- (NEW) specified by application
        IN   securityModel           -- for the outgoing message
        IN   securityEngineID        -- authoritative SNMP entity
        IN   securityName            -- on behalf of this principal
        IN   securityLevel           -- Level of Security requested
        IN   scopedPDU               -- message (plaintext) payload
        IN   securityStateReference  -- reference to security state
                                     -- information from original
                                     -- request
        OUT  securityParameters      -- filled in by Security Module
        OUT  wholeMsg                -- complete generated message
        OUT  wholeMsgLength          -- length of generated message
        OUT  tmStateReference        -- (NEW) transport info
             )

4.2. Elements of Procedure for Outgoing Messages

 1.  If there is a securityStateReference (Response or Report
     message), then this Security Model uses the cached information
     rather than the information provided by the ASI.  Extract the
     tmStateReference from the securityStateReference cache.  Set the
     tmRequestedSecurityLevel to the value of the extracted
     tmTransportSecurityLevel.  Set the tmSameSecurity parameter in
     the tmStateReference cache to true.  The cachedSecurityData for
     this message can now be discarded.
 2.  If there is no securityStateReference (e.g., a Request-type or
     Notification message), then create a tmStateReference cache.  Set
     tmTransportDomain to the value of transportDomain,
     tmTransportAddress to the value of transportAddress, and
     tmRequestedSecurityLevel to the value of securityLevel.
     (Implementers might optimize by pointing to saved copies of these
     session-specific values.)  Set the transaction-specific
     tmSameSecurity parameter to false.
     If the snmpTsmConfigurationUsePrefix object is set to false, then
     set tmSecurityName to the value of securityName.
     If the snmpTsmConfigurationUsePrefix object is set to true, then
     use the transportDomain to look up the corresponding prefix.
     (Since the securityStateReference stores the tmStateReference
     with the tmSecurityName for the incoming message, and since
     tmSecurityName never has a prefix, the prefix-stripping step only
     occurs when we are not using the securityStateReference).

Harrington & Hardaker Standards Track [Page 11] RFC 5591 Transport Security Model for SNMP June 2009

        If the prefix lookup fails for any reason, then the
        snmpTsmUnknownPrefixes counter is incremented, an error
        indication is returned to the calling module, and message
        processing stops.
        If the lookup succeeds, but there is no prefix in the
        securityName, or the prefix returned does not match the prefix
        in the securityName, or the length of the prefix is less than
        1 or greater than 4 US-ASCII alpha-numeric characters, then
        the snmpTsmInvalidPrefixes counter is incremented, an error
        indication is returned to the calling module, and message
        processing stops.
        Strip the transport-specific prefix and trailing ':' character
        (US-ASCII 0x3a) from the securityName.  Set tmSecurityName to
        the value of securityName.
 3.  Set securityParameters to a zero-length OCTET STRING ('0400').
 4.  Combine the message parts into a wholeMsg and calculate
     wholeMsgLength.
 5.  The wholeMsg, wholeMsgLength, securityParameters, and
     tmStateReference are returned to the calling Message Processing
     Model with the statusInformation set to success.

5. Processing an Incoming SNMP Message

 An error indication might return an OID and value for an incremented
 counter, a value for securityLevel, values for contextEngineID and
 contextName for the counter, and the securityStateReference, if this
 information is available at the point where the error is detected.

5.1. Security Processing for an Incoming Message

 This section describes the procedure followed by the Transport
 Security Model whenever it receives an incoming message from a
 Message Processing Model.  The ASI from a Message Processing Model to
 the Security Subsystem for a received message is:
 statusInformation =  -- errorIndication or success
                          -- error counter OID/value if error
 processIncomingMsg(
 IN   messageProcessingModel    -- typically, SNMP version
 IN   maxMessageSize            -- from the received message
 IN   securityParameters        -- from the received message
 IN   securityModel             -- from the received message
 IN   securityLevel             -- from the received message

Harrington & Hardaker Standards Track [Page 12] RFC 5591 Transport Security Model for SNMP June 2009

 IN   wholeMsg                  -- as received on the wire
 IN   wholeMsgLength            -- length as received on the wire
 IN   tmStateReference          -- (NEW) from the Transport Model
 OUT  securityEngineID          -- authoritative SNMP entity
 OUT  securityName              -- identification of the principal
 OUT  scopedPDU,                -- message (plaintext) payload
 OUT  maxSizeResponseScopedPDU  -- maximum size sender can handle
 OUT  securityStateReference    -- reference to security state
  )                         -- information, needed for response

5.2. Elements of Procedure for Incoming Messages

 1.  Set the securityEngineID to the local snmpEngineID.
 2.  If tmStateReference does not refer to a cache containing values
     for tmTransportDomain, tmTransportAddress, tmSecurityName, and
     tmTransportSecurityLevel, then the snmpTsmInvalidCaches counter
     is incremented, an error indication is returned to the calling
     module, and Security Model processing stops for this message.
 3.  Copy the tmSecurityName to securityName.
     If the snmpTsmConfigurationUsePrefix object is set to true, then
     use the tmTransportDomain to look up the corresponding prefix.
        If the prefix lookup fails for any reason, then the
        snmpTsmUnknownPrefixes counter is incremented, an error
        indication is returned to the calling module, and message
        processing stops.
        If the lookup succeeds but the prefix length is less than 1 or
        greater than 4 octets, then the snmpTsmInvalidPrefixes counter
        is incremented, an error indication is returned to the calling
        module, and message processing stops.
        Set the securityName to be the concatenation of the prefix, a
        ':' character (US-ASCII 0x3a), and the tmSecurityName.
 4.  Compare the value of tmTransportSecurityLevel in the
     tmStateReference cache to the value of the securityLevel
     parameter passed in the processIncomingMsg ASI.  If securityLevel
     specifies privacy (Priv) and tmTransportSecurityLevel specifies
     no privacy (noPriv), or if securityLevel specifies authentication
     (auth) and tmTransportSecurityLevel specifies no authentication
     (noAuth) was provided by the Transport Model, then the
     snmpTsmInadequateSecurityLevels counter is incremented, an error
     indication (unsupportedSecurityLevel) together with the OID and

Harrington & Hardaker Standards Track [Page 13] RFC 5591 Transport Security Model for SNMP June 2009

     value of the incremented counter is returned to the calling
     module, and Transport Security Model processing stops for this
     message.
 5.  The tmStateReference is cached as cachedSecurityData so that a
     possible response to this message will use the same security
     parameters.  Then securityStateReference is set for subsequent
     references to this cached data.
 6.  The scopedPDU component is extracted from the wholeMsg.
 7.  The maxSizeResponseScopedPDU is calculated.  This is the maximum
     size allowed for a scopedPDU for a possible Response message.
 8.  The statusInformation is set to success and a return is made to
     the calling module passing back the OUT parameters as specified
     in the processIncomingMsg ASI.

6. MIB Module Overview

 This MIB module provides objects for use only by the Transport
 Security Model.  It defines a configuration scalar and related error
 counters.

6.1. Structure of the MIB Module

 Objects in this MIB module are arranged into subtrees.  Each subtree
 is organized as a set of related objects.  The overall structure and
 assignment of objects to their subtrees, and the intended purpose of
 each subtree, is shown below.

6.1.1. The snmpTsmStats Subtree

 This subtree contains error counters specific to the Transport
 Security Model.

6.1.2. The snmpTsmConfiguration Subtree

 This subtree contains a configuration object that enables
 administrators to specify if they want a transport domain prefix
 prepended to securityNames for use by applications.

6.2. Relationship to Other MIB Modules

 Some management objects defined in other MIB modules are applicable
 to an entity implementing the Transport Security Model.  In
 particular, it is assumed that an entity implementing the Transport
 Security Model will implement the SNMP-FRAMEWORK-MIB [RFC3411], the

Harrington & Hardaker Standards Track [Page 14] RFC 5591 Transport Security Model for SNMP June 2009

 SNMP-TARGET-MIB [RFC3413], the SNMP-VIEW-BASED-ACM-MIB [RFC3415], and
 the SNMPv2-MIB [RFC3418].  These are not needed to implement the
 SNMP-TSM-MIB.

6.2.1. MIB Modules Required for IMPORTS

 The following MIB module imports items from [RFC2578], [RFC2579], and
 [RFC2580].

7. MIB Module Definition

SNMP-TSM-MIB DEFINITIONS ::= BEGIN

IMPORTS

  MODULE-IDENTITY, OBJECT-TYPE,
  mib-2, Counter32
    FROM SNMPv2-SMI -- RFC2578
  MODULE-COMPLIANCE, OBJECT-GROUP
    FROM SNMPv2-CONF -- RFC2580
  TruthValue
     FROM SNMPv2-TC -- RFC2579
  ;

snmpTsmMIB MODULE-IDENTITY

  LAST-UPDATED "200906090000Z"
  ORGANIZATION "ISMS Working Group"
  CONTACT-INFO "WG-EMail:   isms@lists.ietf.org
                Subscribe:  isms-request@lists.ietf.org
                Chairs:
                  Juergen Quittek
                  NEC Europe Ltd.
                  Network Laboratories
                  Kurfuersten-Anlage 36
                  69115 Heidelberg
                  Germany
                  +49 6221 90511-15
                  quittek@netlab.nec.de
                  Juergen Schoenwaelder
                  Jacobs University Bremen
                  Campus Ring 1
                  28725 Bremen
                  Germany
                  +49 421 200-3587
                  j.schoenwaelder@jacobs-university.de

Harrington & Hardaker Standards Track [Page 15] RFC 5591 Transport Security Model for SNMP June 2009

                Editor:
                  David Harrington
                  Huawei Technologies USA
                  1700 Alma Dr.
                  Plano TX 75075
                  USA
                  +1 603-436-8634
                  ietfdbh@comcast.net
                  Wes Hardaker
                  Cobham Analytic Solutions
                  P.O. Box 382
                  Davis, CA  95617
                  USA
                  +1 530 792 1913
                  ietf@hardakers.net
               "
  DESCRIPTION
     "The Transport Security Model MIB.
      In keeping with the RFC 3411 design decisions to use
      self-contained documents, the RFC that contains the definition
      of this MIB module also includes the elements of procedure
      that are needed for processing the Transport Security Model
      for SNMP.  These MIB objects SHOULD NOT be modified via other
      subsystems or models defined in other documents.  This allows
      the Transport Security Model for SNMP to be designed and
      documented as independent and self-contained, having no direct
      impact on other modules, and this allows this module to be
      upgraded and supplemented as the need arises, and to move
      along the standards track on different time-lines from other
      modules.
      Copyright (c) 2009 IETF Trust and the persons
      identified as authors of the code.  All rights reserved.
      Redistribution and use in source and binary forms, with or
      without modification, are permitted provided that the
      following conditions are met:
  1. Redistributions of source code must retain the above copyright

notice, this list of conditions and the following disclaimer.

  1. Redistributions in binary form must reproduce the above

copyright notice, this list of conditions and the following

        disclaimer in the documentation and/or other materials
        provided with the distribution.

Harrington & Hardaker Standards Track [Page 16] RFC 5591 Transport Security Model for SNMP June 2009

  1. Neither the name of Internet Society, IETF or IETF Trust,

nor the names of specific contributors, may be used to endorse

        or promote products derived from this software without
        specific prior written permission.
      THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
      CONTRIBUTORS 'AS IS' AND ANY EXPRESS OR IMPLIED WARRANTIES,
      INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
      MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
      DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
      CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
      SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
      NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
      LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
      HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
      CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
      OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
      EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
      This version of this MIB module is part of RFC 5591;
      see the RFC itself for full legal notices."
  REVISION    "200906090000Z"
  DESCRIPTION "The initial version, published in RFC 5591."
  ::= { mib-2 190 }

– ———————————————————- – – subtrees in the SNMP-TSM-MIB – ———————————————————- –

snmpTsmNotifications OBJECT IDENTIFIER ::= { snmpTsmMIB 0 } snmpTsmMIBObjects OBJECT IDENTIFIER ::= { snmpTsmMIB 1 } snmpTsmConformance OBJECT IDENTIFIER ::= { snmpTsmMIB 2 }

– ————————————————————- – Objects – ————————————————————-

– Statistics for the Transport Security Model

snmpTsmStats OBJECT IDENTIFIER ::= { snmpTsmMIBObjects 1 }

snmpTsmInvalidCaches OBJECT-TYPE

  SYNTAX       Counter32
  MAX-ACCESS   read-only
  STATUS       current
  DESCRIPTION "The number of incoming messages dropped because the

Harrington & Hardaker Standards Track [Page 17] RFC 5591 Transport Security Model for SNMP June 2009

               tmStateReference referred to an invalid cache.
              "
  ::= { snmpTsmStats 1 }

snmpTsmInadequateSecurityLevels OBJECT-TYPE

  SYNTAX       Counter32
  MAX-ACCESS   read-only
  STATUS       current
  DESCRIPTION "The number of incoming messages dropped because
               the securityLevel asserted by the Transport Model was
               less than the securityLevel requested by the
               application.
              "
  ::= { snmpTsmStats 2 }

snmpTsmUnknownPrefixes OBJECT-TYPE

  SYNTAX       Counter32
  MAX-ACCESS   read-only
  STATUS       current
  DESCRIPTION "The number of messages dropped because
               snmpTsmConfigurationUsePrefix was set to true and
               there is no known prefix for the specified transport
               domain.
              "
  ::= { snmpTsmStats 3 }

snmpTsmInvalidPrefixes OBJECT-TYPE

  SYNTAX       Counter32
  MAX-ACCESS   read-only
  STATUS       current
  DESCRIPTION "The number of messages dropped because
               the securityName associated with an outgoing message
               did not contain a valid transport domain prefix.
              "
  ::= { snmpTsmStats 4 }

– ————————————————————- – Configuration – ————————————————————-

– Configuration for the Transport Security Model

snmpTsmConfiguration OBJECT IDENTIFIER ::= { snmpTsmMIBObjects 2 }

snmpTsmConfigurationUsePrefix OBJECT-TYPE

  SYNTAX      TruthValue
  MAX-ACCESS  read-write
  STATUS      current

Harrington & Hardaker Standards Track [Page 18] RFC 5591 Transport Security Model for SNMP June 2009

  DESCRIPTION "If this object is set to true, then securityNames
               passing to and from the application are expected to
               contain a transport-domain-specific prefix.  If this
               object is set to true, then a domain-specific prefix
               will be added by the TSM to the securityName for
               incoming messages and removed from the securityName
               when processing outgoing messages.  Transport domains
               and prefixes are maintained in a registry by IANA.
               This object SHOULD persist across system reboots.
              "
  DEFVAL { false }
  ::= { snmpTsmConfiguration 1 }

– ————————————————————- – snmpTsmMIB - Conformance Information – ————————————————————-

snmpTsmCompliances OBJECT IDENTIFIER ::= { snmpTsmConformance 1 }

snmpTsmGroups OBJECT IDENTIFIER ::= { snmpTsmConformance 2 }

– ————————————————————- – Compliance statements – ————————————————————-

snmpTsmCompliance MODULE-COMPLIANCE

  STATUS      current
  DESCRIPTION "The compliance statement for SNMP engines that support
               the SNMP-TSM-MIB.
              "
  MODULE
      MANDATORY-GROUPS { snmpTsmGroup }
  ::= { snmpTsmCompliances 1 }

– ————————————————————- – Units of conformance – ————————————————————- snmpTsmGroup OBJECT-GROUP

  OBJECTS {
      snmpTsmInvalidCaches,
      snmpTsmInadequateSecurityLevels,
      snmpTsmUnknownPrefixes,
      snmpTsmInvalidPrefixes,
      snmpTsmConfigurationUsePrefix
  }
  STATUS      current
  DESCRIPTION "A collection of objects for maintaining
               information of an SNMP engine that implements

Harrington & Hardaker Standards Track [Page 19] RFC 5591 Transport Security Model for SNMP June 2009

               the SNMP Transport Security Model.
              "
  ::= { snmpTsmGroups 2 }

END

8. Security Considerations

 This document describes a Security Model, compatible with the RFC
 3411 architecture, that permits SNMP to utilize security services
 provided through an SNMP Transport Model.  The Transport Security
 Model relies on Transport Models for mutual authentication, binding
 of keys, confidentiality, and integrity.
 The Transport Security Model relies on secure Transport Models to
 provide an authenticated principal identifier and an assertion of
 whether authentication and privacy are used during transport.  This
 Security Model SHOULD always be used with Transport Models that
 provide adequate security, but "adequate security" is a configuration
 and/or run-time decision of the operator or management application.
 The security threats and how these threats are mitigated should be
 covered in detail in the specifications of the Transport Models and
 the underlying secure transports.
 An authenticated principal identifier (securityName) is used in SNMP
 applications for purposes such as access control, notification
 generation, and proxy forwarding.  This Security Model supports
 multiple Transport Models.  Operators might judge some transports to
 be more secure than others, so this Security Model can be configured
 to prepend a prefix to the securityName to indicate the Transport
 Model used to authenticate the principal.  Operators can use the
 prefixed securityName when making application decisions about levels
 of access.

8.1. MIB Module Security

 There are a number of management objects defined in this MIB module
 with a MAX-ACCESS clause of read-write and/or read-create.  Such
 objects may be considered sensitive or vulnerable in some network
 environments.  The support for SET operations in a non-secure
 environment without proper protection can have a negative effect on
 network operations.  These are the tables and objects and their
 sensitivity/vulnerability:

Harrington & Hardaker Standards Track [Page 20] RFC 5591 Transport Security Model for SNMP June 2009

 o  The snmpTsmConfigurationUsePrefix object could be modified,
    creating a denial of service or authorizing SNMP messages that
    would not have previously been authorized by an Access Control
    Model (e.g., the View-based Access Control Model (VACM)).
 Some of the readable objects in this MIB module (i.e., objects with a
 MAX-ACCESS other than not-accessible) may be considered sensitive or
 vulnerable in some network environments.  It is thus important to
 control even GET and/or NOTIFY access to these objects and possibly
 to even encrypt the values of these objects when sending them over
 the network via SNMP.  These are the tables and objects and their
 sensitivity/vulnerability:
 o  All the counters in this module refer to configuration errors and
    do not expose sensitive information.
 SNMP versions prior to SNMPv3 did not include adequate security.
 Even if the network itself is secure (for example by using IPsec),
 even then, there is no control as to who on the secure network is
 allowed to access and GET/SET (read/change/create/delete) the objects
 in this MIB module.
 It is RECOMMENDED that implementers consider the security features as
 provided by the SNMPv3 framework (see [RFC3410], section 8),
 including full support for the USM and Transport Security Model
 cryptographic mechanisms (for authentication and privacy).
 Further, deployment of SNMP versions prior to SNMPv3 is NOT
 RECOMMENDED.  Instead, it is RECOMMENDED to deploy SNMPv3 and to
 enable cryptographic security.  It is then a customer/operator
 responsibility to ensure that the SNMP entity giving access to an
 instance of this MIB module is properly configured to give access to
 the objects only to those principals (users) that have legitimate
 rights to indeed GET or SET (change/create/delete) them.

9. IANA Considerations

 IANA has assigned:
 1.  An SMI number (190) with a prefix of mib-2 in the MIB module
     registry for the MIB module in this document.
 2.  A value (4) to identify the Transport Security Model, in the
     Security Models registry of the SNMP Number Spaces registry.
     This results in the following table of values:

Harrington & Hardaker Standards Track [Page 21] RFC 5591 Transport Security Model for SNMP June 2009

 Value   Description                         References
 -----   -----------                         ----------
   0     reserved for 'any'                  [RFC3411]
   1     reserved for SNMPv1                 [RFC3411]
   2     reserved for SNMPv2c                [RFC3411]
   3     User-Based Security Model (USM)     [RFC3411]
   4     Transport Security Model (TSM)      [RFC5591]

10. Acknowledgments

 The editors would like to thank Jeffrey Hutzelman for sharing his SSH
 insights and Dave Shield for an outstanding job wordsmithing the
 existing document to improve organization and clarity.
 Additionally, helpful document reviews were received from Juergen
 Schoenwaelder.

11. References

11.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC2578]  McCloghrie, K., Ed., Perkins, D., Ed., and J.
            Schoenwaelder, Ed., "Structure of Management Information
            Version 2 (SMIv2)", STD 58, RFC 2578, April 1999.
 [RFC2579]  McCloghrie, K., Ed., Perkins, D., Ed., and J.
            Schoenwaelder, Ed., "Textual Conventions for SMIv2",
            STD 58, RFC 2579, April 1999.
 [RFC2580]  McCloghrie, K., Perkins, D., and J. Schoenwaelder,
            "Conformance Statements for SMIv2", STD 58, RFC 2580,
            April 1999.
 [RFC3411]  Harrington, D., Presuhn, R., and B. Wijnen, "An
            Architecture for Describing Simple Network Management
            Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
            December 2002.
 [RFC3412]  Case, J., Harrington, D., Presuhn, R., and B. Wijnen,
            "Message Processing and Dispatching for the Simple Network
            Management Protocol (SNMP)", STD 62, RFC 3412,
            December 2002.

Harrington & Hardaker Standards Track [Page 22] RFC 5591 Transport Security Model for SNMP June 2009

 [RFC3413]  Levi, D., Meyer, P., and B. Stewart, "Simple Network
            Management Protocol (SNMP) Applications", STD 62,
            RFC 3413, December 2002.
 [RFC3414]  Blumenthal, U. and B. Wijnen, "User-based Security Model
            (USM) for version 3 of the Simple Network Management
            Protocol (SNMPv3)", STD 62, RFC 3414, December 2002.
 [RFC5590]  Harrington, D. and J. Schoenwaelder, "Transport Subsystem
            for the Simple Network Management Protocol (SNMP)",
            RFC 5590, June 2009.

11.2. Informative References

 [RFC3410]  Case, J., Mundy, R., Partain, D., and B. Stewart,
            "Introduction and Applicability Statements for Internet-
            Standard Management Framework", RFC 3410, December 2002.
 [RFC3415]  Wijnen, B., Presuhn, R., and K. McCloghrie, "View-based
            Access Control Model (VACM) for the Simple Network
            Management Protocol (SNMP)", STD 62, RFC 3415,
            December 2002.
 [RFC3418]  Presuhn, R., "Management Information Base (MIB) for the
            Simple Network Management Protocol (SNMP)", STD 62,
            RFC 3418, December 2002.
 [RFC3584]  Frye, R., Levi, D., Routhier, S., and B. Wijnen,
            "Coexistence between Version 1, Version 2, and Version 3
            of the Internet-standard Network Management Framework",
            BCP 74, RFC 3584, August 2003.
 [RFC5592]  Harrington, D., Salowey, J., and W. Hardaker, "Secure
            Shell Transport Model for the Simple Network Management
            Protocol (SNMP)", RFC 5592, June 2009.

Harrington & Hardaker Standards Track [Page 23] RFC 5591 Transport Security Model for SNMP June 2009

Appendix A. Notification Tables Configuration

 The SNMP-TARGET-MIB and SNMP-NOTIFICATION-MIB [RFC3413] are used to
 configure notification originators with the destinations to which
 notifications should be sent.
 Most of the configuration is Security-Model-independent and
 Transport-Model-independent.
 The values we will use in the examples for the five model-independent
 security and transport parameters are:
    transportDomain = snmpSSHDomain
    transportAddress = 192.0.2.1:5162
    securityModel = Transport Security Model
    securityName = alice
    securityLevel = authPriv
 The following example will configure the notification originator to
 send informs to a notification receiver at 192.0.2.1:5162 using the
 securityName "alice". "alice" is the name for the recipient from the
 standpoint of the notification originator and is used for processing
 access controls before sending a notification.
 The columns marked with an "*" are the items that are Security-Model-
 specific or Transport-Model-specific.
 The configuration for the "alice" settings in the SNMP-VIEW-BASED-
 ACM-MIB objects are not shown here for brevity.  First, we configure
 which type of notification will be sent for this taglist (toCRTag).
 In this example, we choose to send an Inform.
   snmpNotifyTable row:
        snmpNotifyName                 CRNotif
        snmpNotifyTag                  toCRTag
        snmpNotifyType                 inform
        snmpNotifyStorageType          nonVolatile
        snmpNotifyColumnStatus         createAndGo
 Then we configure a transport address to which notifications
 associated with this taglist will be sent, and we specify which
 snmpTargetParamsEntry will be used (toCR) when sending to this
 transport address.

Harrington & Hardaker Standards Track [Page 24] RFC 5591 Transport Security Model for SNMP June 2009

        snmpTargetAddrTable row:
           snmpTargetAddrName              toCRAddr
       *   snmpTargetAddrTDomain           snmpSSHDomain
       *   snmpTargetAddrTAddress          192.0.2.1:5162
           snmpTargetAddrTimeout           1500
           snmpTargetAddrRetryCount        3
           snmpTargetAddrTagList           toCRTag
           snmpTargetAddrParams            toCR   (MUST match below)
           snmpTargetAddrStorageType       nonVolatile
           snmpTargetAddrColumnStatus      createAndGo
 Then we configure which principal at the host will receive the
 notifications associated with this taglist.  Here, we choose "alice",
 who uses the Transport Security Model.
       snmpTargetParamsTable row:
           snmpTargetParamsName            toCR
           snmpTargetParamsMPModel         SNMPv3
       *   snmpTargetParamsSecurityModel   TransportSecurityModel
           snmpTargetParamsSecurityName    "alice"
           snmpTargetParamsSecurityLevel   authPriv
           snmpTargetParamsStorageType     nonVolatile
           snmpTargetParamsRowStatus       createAndGo

A.1. Transport Security Model Processing for Notifications

 The Transport Security Model is called using the generateRequestMsg()
 ASI, with the following parameters (those with an * are from the
 above tables):
  statusInformation =                -- success or errorIndication
        generateRequestMsg(
        IN   messageProcessingModel  -- *snmpTargetParamsMPModel
        IN   globalData              -- message header, admin data
        IN   maxMessageSize          -- of the sending SNMP entity
        IN   transportDomain         -- *snmpTargetAddrTDomain
        IN   transportAddress        -- *snmpTargetAddrTAddress
        IN   securityModel           -- *snmpTargetParamsSecurityModel
        IN   securityEngineID        -- immaterial; TSM will ignore.
        IN   securityName            -- snmpTargetParamsSecurityName
        IN   securityLevel           -- *snmpTargetParamsSecurityLevel
        IN   scopedPDU               -- message (plaintext) payload
        OUT  securityParameters      -- filled in by Security Module
        OUT  wholeMsg                -- complete generated message
        OUT  wholeMsgLength          -- length of generated message
        OUT  tmStateReference        -- reference to transport info
             )

Harrington & Hardaker Standards Track [Page 25] RFC 5591 Transport Security Model for SNMP June 2009

 The Transport Security Model will determine the Transport Model based
 on the snmpTargetAddrTDomain.  The selected Transport Model will
 select the appropriate transport connection using the
 tmStateReference cache created from the values of
 snmpTargetAddrTAddress, snmpTargetParamsSecurityName, and
 snmpTargetParamsSecurityLevel.

Appendix B. Processing Differences between USM and Secure Transport

 USM and secure transports differ in the processing order and
 responsibilities within the RFC 3411 architecture.  While the steps
 are the same, they occur in a different order and might be done by
 different subsystems.  The following lists illustrate the difference
 in the flow and the responsibility for different processing steps for
 incoming messages when using USM and when using a secure transport.
 (These lists are simplified for illustrative purposes, and do not
 represent all details of processing.  Transport Models MUST provide
 the detailed elements of procedure.)
 With USM, SNMPv1, and SNMPv2c Security Models, security processing
 starts when the Message Processing Model decodes portions of the
 ASN.1 message to extract header fields that are used to determine
 which Security Model will process the message to perform
 authentication, decryption, timeliness checking, integrity checking,
 and translation of parameters to model-independent parameters.  By
 comparison, a secure transport performs those security functions on
 the message, before the ASN.1 is decoded.
 Step 6 cannot occur until after decryption occurs.  Steps 6 and
 beyond are the same for USM and a secure transport.

B.1. USM and the RFC 3411 Architecture

 1) Decode the ASN.1 header (Message Processing Model).
 2) Determine the SNMP Security Model and parameters (Message
    Processing Model).
 3) Verify securityLevel (Security Model).
 4) Translate parameters to model-independent parameters (Security
    Model).
 5) Authenticate the principal, check message integrity and
    timeliness, and decrypt the message (Security Model).

Harrington & Hardaker Standards Track [Page 26] RFC 5591 Transport Security Model for SNMP June 2009

 6) Determine the pduType in the decrypted portions (Message
    Processing Model).
 7) Pass on the decrypted portions with model-independent parameters.

B.2. Transport Subsystem and the RFC 3411 Architecture

 1) Authenticate the principal, check integrity and timeliness of the
    message, and decrypt the message (Transport Model).
 2) Translate parameters to model-independent parameters (Transport
    Model).
 3) Decode the ASN.1 header (Message Processing Model).
 4) Determine the SNMP Security Model and parameters (Message
    Processing Model).
 5) Verify securityLevel (Security Model).
 6) Determine the pduType in the decrypted portions (Message
    Processing Model).
 7) Pass on the decrypted portions with model-independent security
    parameters.
 If a message is secured using a secure transport layer, then the
 Transport Model will provide the translation from the authenticated
 identity (e.g., an SSH user name) to a human-friendly identifier
 (tmSecurityName) in step 2.  The Security Model will provide a
 mapping from that identifier to a model-independent securityName.

Harrington & Hardaker Standards Track [Page 27] RFC 5591 Transport Security Model for SNMP June 2009

Authors' Addresses

 David Harrington
 Huawei Technologies (USA)
 1700 Alma Dr. Suite 100
 Plano, TX 75075
 USA
 Phone: +1 603 436 8634
 EMail: ietfdbh@comcast.net
 Wes Hardaker
 Cobham Analytic Solutions
 P.O. Box 382
 Davis, CA  95617
 US
 Phone: +1 530 792 1913
 EMail: ietf@hardakers.net

Harrington & Hardaker Standards Track [Page 28]

Internet Engineering Task Force (IETF) W. Hardaker Request for Comments: 6353 SPARTA, Inc. Obsoletes: 5953 July 2011 Category: Standards Track ISSN: 2070-1721

         Transport Layer Security (TLS) Transport Model for
           the Simple Network Management Protocol (SNMP)

Abstract

 This document describes a Transport Model for the Simple Network
 Management Protocol (SNMP), that uses either the Transport Layer
 Security protocol or the Datagram Transport Layer Security (DTLS)
 protocol.  The TLS and DTLS protocols provide authentication and
 privacy services for SNMP applications.  This document describes how
 the TLS Transport Model (TLSTM) implements the needed features of an
 SNMP Transport Subsystem to make this protection possible in an
 interoperable way.
 This Transport Model is designed to meet the security and operational
 needs of network administrators.  It supports the sending of SNMP
 messages over TLS/TCP and DTLS/UDP.  The TLS mode can make use of
 TCP's improved support for larger packet sizes and the DTLS mode
 provides potentially superior operation in environments where a
 connectionless (e.g., UDP) transport is preferred.  Both TLS and DTLS
 integrate well into existing public keying infrastructures.
 This document also defines a portion of the Management Information
 Base (MIB) for use with network management protocols.  In particular,
 it defines objects for managing the TLS Transport Model for SNMP.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6353.

Hardaker Standards Track [Page 1] RFC 6353 TLS Transport Model for SNMP July 2011

Copyright Notice

 Copyright (c) 2011 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.
 This document may contain material from IETF Documents or IETF
 Contributions published or made publicly available before November
 10, 2008.  The person(s) controlling the copyright in some of this
 material may not have granted the IETF Trust the right to allow
 modifications of such material outside the IETF Standards Process.
 Without obtaining an adequate license from the person(s) controlling
 the copyright in such materials, this document may not be modified
 outside the IETF Standards Process, and derivative works of it may
 not be created outside the IETF Standards Process, except to format
 it for publication as an RFC or to translate it into languages other
 than English.

Table of Contents

 1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   1.1.  Conventions  . . . . . . . . . . . . . . . . . . . . . . .  7
   1.2.  Changes Since RFC 5953 . . . . . . . . . . . . . . . . . .  8
 2.  The Transport Layer Security Protocol  . . . . . . . . . . . .  8
 3.  How the TLSTM Fits into the Transport Subsystem  . . . . . . .  8
   3.1.  Security Capabilities of This Model  . . . . . . . . . . . 11
     3.1.1.  Threats  . . . . . . . . . . . . . . . . . . . . . . . 11
     3.1.2.  Message Protection . . . . . . . . . . . . . . . . . . 12
     3.1.3.  (D)TLS Connections . . . . . . . . . . . . . . . . . . 13
   3.2.  Security Parameter Passing . . . . . . . . . . . . . . . . 14
   3.3.  Notifications and Proxy  . . . . . . . . . . . . . . . . . 14
 4.  Elements of the Model  . . . . . . . . . . . . . . . . . . . . 15
   4.1.  X.509 Certificates . . . . . . . . . . . . . . . . . . . . 15
     4.1.1.  Provisioning for the Certificate . . . . . . . . . . . 15
   4.2.  (D)TLS Usage . . . . . . . . . . . . . . . . . . . . . . . 17
   4.3.  SNMP Services  . . . . . . . . . . . . . . . . . . . . . . 18
     4.3.1.  SNMP Services for an Outgoing Message  . . . . . . . . 18
     4.3.2.  SNMP Services for an Incoming Message  . . . . . . . . 19

Hardaker Standards Track [Page 2] RFC 6353 TLS Transport Model for SNMP July 2011

   4.4.  Cached Information and References  . . . . . . . . . . . . 20
     4.4.1.  TLS Transport Model Cached Information . . . . . . . . 20
       4.4.1.1.  tmSecurityName . . . . . . . . . . . . . . . . . . 20
       4.4.1.2.  tmSessionID  . . . . . . . . . . . . . . . . . . . 21
       4.4.1.3.  Session State  . . . . . . . . . . . . . . . . . . 21
 5.  Elements of Procedure  . . . . . . . . . . . . . . . . . . . . 21
   5.1.  Procedures for an Incoming Message . . . . . . . . . . . . 21
     5.1.1.  DTLS over UDP Processing for Incoming Messages . . . . 22
     5.1.2.  Transport Processing for Incoming SNMP Messages  . . . 23
   5.2.  Procedures for an Outgoing SNMP Message  . . . . . . . . . 25
   5.3.  Establishing or Accepting a Session  . . . . . . . . . . . 26
     5.3.1.  Establishing a Session as a Client . . . . . . . . . . 26
     5.3.2.  Accepting a Session as a Server  . . . . . . . . . . . 28
   5.4.  Closing a Session  . . . . . . . . . . . . . . . . . . . . 29
 6.  MIB Module Overview  . . . . . . . . . . . . . . . . . . . . . 30
   6.1.  Structure of the MIB Module  . . . . . . . . . . . . . . . 30
   6.2.  Textual Conventions  . . . . . . . . . . . . . . . . . . . 30
   6.3.  Statistical Counters . . . . . . . . . . . . . . . . . . . 30
   6.4.  Configuration Tables . . . . . . . . . . . . . . . . . . . 30
     6.4.1.  Notifications  . . . . . . . . . . . . . . . . . . . . 31
   6.5.  Relationship to Other MIB Modules  . . . . . . . . . . . . 31
     6.5.1.  MIB Modules Required for IMPORTS . . . . . . . . . . . 31
 7.  MIB Module Definition  . . . . . . . . . . . . . . . . . . . . 31
 8.  Operational Considerations . . . . . . . . . . . . . . . . . . 54
   8.1.  Sessions . . . . . . . . . . . . . . . . . . . . . . . . . 54
   8.2.  Notification Receiver Credential Selection . . . . . . . . 54
   8.3.  contextEngineID Discovery  . . . . . . . . . . . . . . . . 55
   8.4.  Transport Considerations . . . . . . . . . . . . . . . . . 55
 9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 55
   9.1.  Certificates, Authentication, and Authorization  . . . . . 55
   9.2.  (D)TLS Security Considerations . . . . . . . . . . . . . . 56
     9.2.1.  TLS Version Requirements . . . . . . . . . . . . . . . 56
     9.2.2.  Perfect Forward Secrecy  . . . . . . . . . . . . . . . 57
   9.3.  Use with SNMPv1/SNMPv2c Messages . . . . . . . . . . . . . 57
   9.4.  MIB Module Security  . . . . . . . . . . . . . . . . . . . 57
 10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 59
 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 59
 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 60
   12.1. Normative References . . . . . . . . . . . . . . . . . . . 60
   12.2. Informative References . . . . . . . . . . . . . . . . . . 61
 Appendix A.  Target and Notification Configuration Example . . . . 63
   A.1.  Configuring a Notification Originator  . . . . . . . . . . 63
   A.2.  Configuring TLSTM to Utilize a Simple Derivation of
         tmSecurityName . . . . . . . . . . . . . . . . . . . . . . 64
   A.3.  Configuring TLSTM to Utilize Table-Driven Certificate
         Mapping  . . . . . . . . . . . . . . . . . . . . . . . . . 64

Hardaker Standards Track [Page 3] RFC 6353 TLS Transport Model for SNMP July 2011

1. Introduction

 It is important to understand the modular SNMPv3 architecture as
 defined by [RFC3411] and enhanced by the Transport Subsystem
 [RFC5590].  It is also important to understand the terminology of the
 SNMPv3 architecture in order to understand where the Transport Model
 described in this document fits into the architecture and how it
 interacts with the other architecture subsystems.  For a detailed
 overview of the documents that describe the current Internet-Standard
 Management Framework, please refer to Section 7 of [RFC3410].
 This document describes a Transport Model that makes use of the
 Transport Layer Security (TLS) [RFC5246] and the Datagram Transport
 Layer Security (DTLS) Protocol [RFC4347], within a Transport
 Subsystem [RFC5590].  DTLS is the datagram variant of the Transport
 Layer Security (TLS) protocol [RFC5246].  The Transport Model in this
 document is referred to as the Transport Layer Security Transport
 Model (TLSTM).  TLS and DTLS take advantage of the X.509 public
 keying infrastructure [RFC5280].  While (D)TLS supports multiple
 authentication mechanisms, this document only discusses X.509
 certificate-based authentication.  Although other forms of
 authentication are possible, they are outside the scope of this
 specification.  This transport model is designed to meet the security
 and operational needs of network administrators, operating in both
 environments where a connectionless (e.g., UDP) transport is
 preferred and in environments where large quantities of data need to
 be sent (e.g., over a TCP-based stream).  Both TLS and DTLS integrate
 well into existing public keying infrastructures.  This document
 supports sending of SNMP messages over TLS/TCP and DTLS/UDP.
 This document also defines a portion of the Management Information
 Base (MIB) for use with network management protocols.  In particular,
 it defines objects for managing the TLS Transport Model for SNMP.
 Managed objects are accessed via a virtual information store, termed
 the Management Information Base or MIB.  MIB objects are generally
 accessed through the Simple Network Management Protocol (SNMP).
 Objects in the MIB are defined using the mechanisms defined in the
 Structure of Management Information (SMI).  This memo specifies a MIB
 module that is compliant to the SMIv2, which is described in STD 58:
 [RFC2578], [RFC2579], and [RFC2580].

Hardaker Standards Track [Page 4] RFC 6353 TLS Transport Model for SNMP July 2011

 The diagram shown below gives a conceptual overview of two SNMP
 entities communicating using the TLS Transport Model (shown as
 "TLSTM").  One entity contains a command responder and notification
 originator application, and the other a command generator and
 notification receiver application.  It should be understood that this
 particular mix of application types is an example only and other
 combinations are equally valid.
 Note: this diagram shows the Transport Security Model (TSM) being
 used as the security model that is defined in [RFC5591].

Hardaker Standards Track [Page 5] RFC 6353 TLS Transport Model for SNMP July 2011

+———————————————————————+ | Network | +———————————————————————+

   ^                     |            ^               |
   |Notifications        |Commands    |Commands       |Notifications

+—|———————|——-+ +–|—————|————–+ | | V | | | V | | +————+ +————+ | | +———–+ +———-+ | | | (D)TLS | | (D)TLS | | | | (D)TLS | | (D)TLS | | | | (Client) | | (Server) | | | | (Client) | | (Server) | | | +————+ +————+ | | +———–+ +———-+ | | ^ ^ | | ^ ^ | | | | | | | | | | +————-+ | | +————–+ | | +—–|————+ | | +—–|————+ | | | V | | | | V | | | | +——–+ | +—–+ | | | +——–+ | +—–+ | | | | TLS TM |←——–>|Cache| | | | | TLS TM |←——–>|Cache| | | | +——–+ | +—–+ | | | +——–+ | +—–+ | | |Transport Subsys. | ^ | | |Transport Subsys. | ^ | | +——————+ | | | +——————+ | | | ^ | | | ^ | | | | +–+ | | | +–+ | | v | | | V | | | +—–+ +——–+ +——-+ | | | +—–+ +——–+ +——-+ | | | | | |Message | |Securi.| | | | | | |Message | |Securi.| | | | |Disp.| |Proc. | |Subsys.| | | | |Disp.| |Proc. | |Subsys.| | | | | | |Subsys. | | | | | | | | |Subsys. | | | | | | | | | | | | | | | | | | | | | | | | | | | +—-+ | | +—+ | | | | | | | +—-+ | | +—+ | | | | | ←–>|v3MP|←→ |TSM|←-+ | | | ←–>|v3MP|←–>|TSM|←-+ | | | | | +—-+ | | +—+ | | | | | | +—-+ | | +—+ | | | | | | | | | | | | | | | | | | | +—–+ +——–+ +——-+ | | +—–+ +——–+ +——-+ | | ^ | | ^ | | | | | | | | +-+————+ | | +-+———-+ | | | | | | | | | | v v | | v V | | +————-+ +————-+ | | +————-+ +————-+ | | | COMMAND | | NOTIFICAT. | | | | COMMAND | | NOTIFICAT. | | | | RESPONDER | | ORIGINATOR | | | | GENERATOR | | RECEIVER | | | | application | | application | | | | application | | application | | | +————-+ +————-+ | | +————-+ +————-+ | | SNMP entity | | SNMP entity | +———————————+ +———————————+

Hardaker Standards Track [Page 6] RFC 6353 TLS Transport Model for SNMP July 2011

1.1. Conventions

 For consistency with SNMP-related specifications, this document
 favors terminology as defined in STD 62, rather than favoring
 terminology that is consistent with non-SNMP specifications.  This is
 consistent with the IESG decision to not require the SNMPv3
 terminology be modified to match the usage of other non-SNMP
 specifications when SNMPv3 was advanced to a Full Standard.
 "Authentication" in this document typically refers to the English
 meaning of "serving to prove the authenticity of" the message, not
 data source authentication or peer identity authentication.
 The terms "manager" and "agent" are not used in this document
 because, in the [RFC3411] architecture, all SNMP entities have the
 capability of acting as manager, agent, or both depending on the SNMP
 application types supported in the implementation.  Where distinction
 is required, the application names of command generator, command
 responder, notification originator, notification receiver, and proxy
 forwarder are used.  See "SNMP Applications" [RFC3413] for further
 information.
 Large portions of this document simultaneously refer to both TLS and
 DTLS when discussing TLSTM components that function equally with
 either protocol.  "(D)TLS" is used in these places to indicate that
 the statement applies to either or both protocols as appropriate.
 When a distinction between the protocols is needed, they are referred
 to independently through the use of "TLS" or "DTLS".  The Transport
 Model, however, is named "TLS Transport Model" and refers not to the
 TLS or DTLS protocol but to the specification in this document, which
 includes support for both TLS and DTLS.
 Throughout this document, the terms "client" and "server" are used to
 refer to the two ends of the (D)TLS transport connection.  The client
 actively opens the (D)TLS connection, and the server passively
 listens for the incoming (D)TLS connection.  An SNMP entity may act
 as a (D)TLS client or server or both, depending on the SNMP
 applications supported.
 The User-Based Security Model (USM) [RFC3414] is a mandatory-to-
 implement Security Model in STD 62.  While (D)TLS and USM frequently
 refer to a user, the terminology preferred in RFC 3411 and in this
 memo is "principal".  A principal is the "who" on whose behalf
 services are provided or processing takes place.  A principal can be,
 among other things, an individual acting in a particular role; a set
 of individuals, with each acting in a particular role; an application
 or a set of applications, or a combination of these within an
 administrative domain.

Hardaker Standards Track [Page 7] RFC 6353 TLS Transport Model for SNMP July 2011

 Throughout this document, the term "session" is used to refer to a
 secure association between two TLS Transport Models that permits the
 transmission of one or more SNMP messages within the lifetime of the
 session.  The (D)TLS protocols also have an internal notion of a
 session and although these two concepts of a session are related,
 when the term "session" is used this document is referring to the
 TLSTM's specific session and not directly to the (D)TLS protocol's
 session.
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in [RFC2119].

1.2. Changes Since RFC 5953

 This document obsoletes [RFC5953].
 Since the publication of RFC 5953, a few editorial errata have been
 noted.  These errata are posted on the RFC Editor web site.  These
 errors have been corrected in this document.
 This document updates the references to RFC 3490 (IDNA 2003) to
 [RFC5890] (IDNA 2008), because RFC 3490 was obsoleted by RFC 5890.
 References to RFC 1033 were replaced with references to [RFC1123].
 Added informative reference to 5953.
 Updated MIB dates and revision date.

2. The Transport Layer Security Protocol

 (D)TLS provides authentication, data message integrity, and privacy
 at the transport layer (see [RFC4347]).
 The primary goals of the TLS Transport Model are to provide privacy,
 peer identity authentication, and data integrity between two
 communicating SNMP entities.  The TLS and DTLS protocols provide a
 secure transport upon which the TLSTM is based.  Please refer to
 [RFC5246] and [RFC4347] for complete descriptions of the protocols.

3. How the TLSTM Fits into the Transport Subsystem

 A transport model is a component of the Transport Subsystem.  The TLS
 Transport Model thus fits between the underlying (D)TLS transport
 layer and the Message Dispatcher [RFC3411] component of the SNMP
 engine.

Hardaker Standards Track [Page 8] RFC 6353 TLS Transport Model for SNMP July 2011

 The TLS Transport Model will establish a session between itself and
 the TLS Transport Model of another SNMP engine.  The sending
 transport model passes unencrypted and unauthenticated messages from
 the Dispatcher to (D)TLS to be encrypted and authenticated, and the
 receiving transport model accepts decrypted and authenticated/
 integrity-checked incoming messages from (D)TLS and passes them to
 the Dispatcher.
 After a TLS Transport Model session is established, SNMP messages can
 conceptually be sent through the session from one SNMP message
 Dispatcher to another SNMP Message Dispatcher.  If multiple SNMP
 messages are needed to be passed between two SNMP applications they
 MAY be passed through the same session.  A TLSTM implementation
 engine MAY choose to close the session to conserve resources.
 The TLS Transport Model of an SNMP engine will perform the
 translation between (D)TLS-specific security parameters and SNMP-
 specific, model-independent parameters.

Hardaker Standards Track [Page 9] RFC 6353 TLS Transport Model for SNMP July 2011

 The diagram below depicts where the TLS Transport Model (shown as
 "(D)TLS TM") fits into the architecture described in RFC 3411 and the
 Transport Subsystem:
 +------------------------------+
 |    Network                   |
 +------------------------------+
    ^       ^              ^
    |       |              |
    v       v              v
 +-------------------------------------------------------------------+
 | +--------------------------------------------------+              |
 | |  Transport Subsystem                             |  +--------+  |
 | | +-----+ +-----+ +-------+             +-------+  |  |        |  |
 | | | UDP | | SSH | |(D)TLS |    . . .    | other |<--->| Cache  |  |
 | | |     | | TM  | | TM    |             |       |  |  |        |  |
 | | +-----+ +-----+ +-------+             +-------+  |  +--------+  |
 | +--------------------------------------------------+         ^    |
 |              ^                                               |    |
 |              |                                               |    |
 | Dispatcher   v                                               |    |
 | +--------------+ +---------------------+  +----------------+ |    |
 | | Transport    | | Message Processing  |  | Security       | |    |
 | | Dispatch     | | Subsystem           |  | Subsystem      | |    |
 | |              | |     +------------+  |  | +------------+ | |    |
 | |              | |  +->| v1MP       |<--->| | USM        | | |    |
 | |              | |  |  +------------+  |  | +------------+ | |    |
 | |              | |  |  +------------+  |  | +------------+ | |    |
 | |              | |  +->| v2cMP      |<--->| | Transport  | | |    |
 | | Message      | |  |  +------------+  |  | | Security   |<--+    |
 | | Dispatch    <---->|  +------------+  |  | | Model      | |      |
 | |              | |  +->| v3MP       |<--->| +------------+ |      |
 | |              | |  |  +------------+  |  | +------------+ |      |
 | | PDU Dispatch | |  |  +------------+  |  | | Other      | |      |
 | +--------------+ |  +->| otherMP    |<--->| | Model(s)   | |      |
 |              ^   |     +------------+  |  | +------------+ |      |
 |              |   +---------------------+  +----------------+      |
 |              v                                                    |
 |      +-------+-------------------------+---------------+          |
 |      ^                                 ^               ^          |
 |      |                                 |               |          |
 |      v                                 v               v          |

Hardaker Standards Track [Page 10] RFC 6353 TLS Transport Model for SNMP July 2011

 | +-------------+   +---------+   +--------------+  +-------------+ |
 | |   COMMAND   |   | ACCESS  |   | NOTIFICATION |  |    PROXY    | |
 | |  RESPONDER  |<->| CONTROL |<->|  ORIGINATOR  |  |  FORWARDER  | |
 | | application |   |         |   | applications |  | application | |
 | +-------------+   +---------+   +--------------+  +-------------+ |
 |      ^                                 ^                          |
 |      |                                 |                          |
 |      v                                 v                          |
 | +----------------------------------------------+                  |
 | |             MIB instrumentation              |      SNMP entity |
 +-------------------------------------------------------------------+

3.1. Security Capabilities of This Model

3.1.1. Threats

 The TLS Transport Model provides protection against the threats
 identified by the RFC 3411 architecture [RFC3411]:
 1.  Modification of Information - The modification threat is the
     danger that an unauthorized entity may alter in-transit SNMP
     messages generated on behalf of an authorized principal in such a
     way as to effect unauthorized management operations, including
     falsifying the value of an object.
     (D)TLS provides verification that the content of each received
     message has not been modified during its transmission through the
     network, data has not been altered or destroyed in an
     unauthorized manner, and data sequences have not been altered to
     an extent greater than can occur non-maliciously.
 2.  Masquerade - The masquerade threat is the danger that management
     operations unauthorized for a given principal may be attempted by
     assuming the identity of another principal that has the
     appropriate authorizations.
     The TLSTM verifies the identity of the (D)TLS server through the
     use of the (D)TLS protocol and X.509 certificates.  A TLS
     Transport Model implementation MUST support the authentication of
     both the server and the client.
 3.  Message stream modification - The re-ordering, delay, or replay
     of messages can and does occur through the natural operation of
     many connectionless transport services.  The message stream
     modification threat is the danger that messages may be
     maliciously re-ordered, delayed, or replayed to an extent that is
     greater than can occur through the natural operation of

Hardaker Standards Track [Page 11] RFC 6353 TLS Transport Model for SNMP July 2011

     connectionless transport services, in order to effect
     unauthorized management operations.
     (D)TLS provides replay protection with a Message Authentication
     Code (MAC) that includes a sequence number.  Since UDP provides
     no sequencing ability, DTLS uses a sliding window protocol with
     the sequence number used for replay protection (see [RFC4347]).
 4.  Disclosure - The disclosure threat is the danger of eavesdropping
     on the exchanges between SNMP engines.
     (D)TLS provides protection against the disclosure of information
     to unauthorized recipients or eavesdroppers by allowing for
     encryption of all traffic between SNMP engines.  A TLS Transport
     Model implementation MUST support message encryption to protect
     sensitive data from eavesdropping attacks.
 5.  Denial of Service - The RFC 3411 architecture [RFC3411] states
     that denial-of-service (DoS) attacks need not be addressed by an
     SNMP security protocol.  However, connectionless transports (like
     DTLS over UDP) are susceptible to a variety of DoS attacks
     because they are more vulnerable to spoofed IP addresses.  See
     Section 4.2 for details on how the cookie mechanism is used.
     Note, however, that this mechanism does not provide any defense
     against DoS attacks mounted from valid IP addresses.
 See Section 9 for more detail on the security considerations
 associated with the TLSTM and these security threats.

3.1.2. Message Protection

 The RFC 3411 architecture recognizes three levels of security:
 o  without authentication and without privacy (noAuthNoPriv)
 o  with authentication but without privacy (authNoPriv)
 o  with authentication and with privacy (authPriv)
 The TLS Transport Model determines from (D)TLS the identity of the
 authenticated principal, the transport type, and the transport
 address associated with an incoming message.  The TLS Transport Model
 provides the identity and destination type and address to (D)TLS for
 outgoing messages.
 When an application requests a session for a message, it also
 requests a security level for that session.  The TLS Transport Model
 MUST ensure that the (D)TLS connection provides security at least as

Hardaker Standards Track [Page 12] RFC 6353 TLS Transport Model for SNMP July 2011

 high as the requested level of security.  How the security level is
 translated into the algorithms used to provide data integrity and
 privacy is implementation dependent.  However, the NULL integrity and
 encryption algorithms MUST NOT be used to fulfill security level
 requests for authentication or privacy.  Implementations MAY choose
 to force (D)TLS to only allow cipher_suites that provide both
 authentication and privacy to guarantee this assertion.
 If a suitable interface between the TLS Transport Model and the
 (D)TLS Handshake Protocol is implemented to allow the selection of
 security-level-dependent algorithms (for example, a security level to
 cipher_suites mapping table), then different security levels may be
 utilized by the application.
 The authentication, integrity, and privacy algorithms used by the
 (D)TLS Protocols may vary over time as the science of cryptography
 continues to evolve and the development of (D)TLS continues over
 time.  Implementers are encouraged to plan for changes in operator
 trust of particular algorithms.  Implementations SHOULD offer
 configuration settings for mapping algorithms to SNMPv3 security
 levels.

3.1.3. (D)TLS Connections

 (D)TLS connections are opened by the TLS Transport Model during the
 elements of procedure for an outgoing SNMP message.  Since the sender
 of a message initiates the creation of a (D)TLS connection if needed,
 the (D)TLS connection will already exist for an incoming message.
 Implementations MAY choose to instantiate (D)TLS connections in
 anticipation of outgoing messages.  This approach might be useful to
 ensure that a (D)TLS connection to a given target can be established
 before it becomes important to send a message over the (D)TLS
 connection.  Of course, there is no guarantee that a pre-established
 session will still be valid when needed.
 DTLS connections, when used over UDP, are uniquely identified within
 the TLS Transport Model by the combination of transportDomain,
 transportAddress, tmSecurityName, and requestedSecurityLevel
 associated with each session.  Each unique combination of these
 parameters MUST have a locally chosen unique tlstmSessionID for each
 active session.  For further information, see Section 5.  TLS over
 TCP sessions, on the other hand, do not require a unique pairing of
 address and port attributes since their lower-layer protocols (TCP)
 already provide adequate session framing.  But they must still
 provide a unique tlstmSessionID for referencing the session.

Hardaker Standards Track [Page 13] RFC 6353 TLS Transport Model for SNMP July 2011

 The tlstmSessionID MUST NOT change during the entire duration of the
 session from the TLSTM's perspective, and MUST uniquely identify a
 single session.  As an implementation hint: note that the (D)TLS
 internal SessionID does not meet these requirements, since it can
 change over the life of the connection as seen by the TLSTM (for
 example, during renegotiation), and does not necessarily uniquely
 identify a TLSTM session (there can be multiple TLSTM sessions
 sharing the same D(TLS) internal SessionID).

3.2. Security Parameter Passing

 For the (D)TLS server-side, (D)TLS-specific security parameters
 (i.e., cipher_suites, X.509 certificate fields, IP addresses, and
 ports) are translated by the TLS Transport Model into security
 parameters for the TLS Transport Model and security model (e.g.,
 tmSecurityLevel, tmSecurityName, transportDomain, transportAddress).
 The transport-related and (D)TLS-security-related information,
 including the authenticated identity, are stored in a cache
 referenced by tmStateReference.
 For the (D)TLS client side, the TLS Transport Model takes input
 provided by the Dispatcher in the sendMessage() Abstract Service
 Interface (ASI) and input from the tmStateReference cache.  The
 (D)TLS Transport Model converts that information into suitable
 security parameters for (D)TLS and establishes sessions as needed.
 The elements of procedure in Section 5 discuss these concepts in much
 greater detail.

3.3. Notifications and Proxy

 (D)TLS connections may be initiated by (D)TLS clients on behalf of
 SNMP applications that initiate communications, such as command
 generators, notification originators, proxy forwarders.  Command
 generators are frequently operated by a human, but notification
 originators and proxy forwarders are usually unmanned automated
 processes.  The targets to whom notifications and proxied requests
 should be sent are typically determined and configured by a network
 administrator.
 The SNMP-TARGET-MIB module [RFC3413] contains objects for defining
 management targets, including transportDomain, transportAddress,
 securityName, securityModel, and securityLevel parameters, for
 notification originator, proxy forwarder, and SNMP-controllable
 command generator applications.  Transport domains and transport
 addresses are configured in the snmpTargetAddrTable, and the
 securityModel, securityName, and securityLevel parameters are
 configured in the snmpTargetParamsTable.  This document defines a MIB

Hardaker Standards Track [Page 14] RFC 6353 TLS Transport Model for SNMP July 2011

 module that extends the SNMP-TARGET-MIB's snmpTargetParamsTable to
 specify a (D)TLS client-side certificate to use for the connection.
 When configuring a (D)TLS target, the snmpTargetAddrTDomain and
 snmpTargetAddrTAddress parameters in snmpTargetAddrTable SHOULD be
 set to the snmpTLSTCPDomain or snmpDTLSUDPDomain object and an
 appropriate snmpTLSAddress value.  When used with the SNMPv3 message
 processing model, the snmpTargetParamsMPModel column of the
 snmpTargetParamsTable SHOULD be set to a value of 3.  The
 snmpTargetParamsSecurityName SHOULD be set to an appropriate
 securityName value, and the snmpTlstmParamsClientFingerprint
 parameter of the snmpTlstmParamsTable SHOULD be set to a value that
 refers to a locally held certificate (and the corresponding private
 key) to be used.  Other parameters, for example, cryptographic
 configuration such as which cipher_suites to use, must come from
 configuration mechanisms not defined in this document.
 The securityName defined in the snmpTargetParamsSecurityName column
 will be used by the access control model to authorize any
 notifications that need to be sent.

4. Elements of the Model

 This section contains definitions required to realize the (D)TLS
 Transport Model defined by this document.

4.1. X.509 Certificates

 (D)TLS can make use of X.509 certificates for authentication of both
 sides of the transport.  This section discusses the use of X.509
 certificates in the TLSTM.
 While (D)TLS supports multiple authentication mechanisms, this
 document only discusses X.509-certificate-based authentication; other
 forms of authentication are outside the scope of this specification.
 TLSTM implementations are REQUIRED to support X.509 certificates.

4.1.1. Provisioning for the Certificate

 Authentication using (D)TLS will require that SNMP entities have
 certificates, either signed by trusted Certification Authorities
 (CAs), or self signed.  Furthermore, SNMP entities will most commonly
 need to be provisioned with root certificates that represent the list
 of trusted CAs that an SNMP entity can use for certificate
 verification.  SNMP entities SHOULD also be provisioned with an X.509
 certificate revocation mechanism which can be used to verify that a
 certificate has not been revoked.  Trusted public keys from either CA
 certificates and/or self-signed certificates MUST be installed into

Hardaker Standards Track [Page 15] RFC 6353 TLS Transport Model for SNMP July 2011

 the server through a trusted out-of-band mechanism and their
 authenticity MUST be verified before access is granted.
 Having received a certificate from a connecting TLSTM client, the
 authenticated tmSecurityName of the principal is derived using the
 snmpTlstmCertToTSNTable.  This table allows mapping of incoming
 connections to tmSecurityNames through defined transformations.  The
 transformations defined in the SNMP-TLS-TM-MIB include:
 o  Mapping a certificate's subjectAltName or CommonName components to
    a tmSecurityName, or
 o  Mapping a certificate's fingerprint value to a directly specified
    tmSecurityName
 As an implementation hint: implementations may choose to discard any
 connections for which no potential snmpTlstmCertToTSNTable mapping
 exists before performing certificate verification to avoid expending
 computational resources associated with certificate verification.
 Deployments SHOULD map the "subjectAltName" component of X.509
 certificates to the TLSTM specific tmSecurityNames.  The
 authenticated identity can be obtained by the TLS Transport Model by
 extracting the subjectAltName(s) from the peer's certificate.  The
 receiving application will then have an appropriate tmSecurityName
 for use by other SNMPv3 components like an access control model.
 An example of this type of mapping setup can be found in Appendix A.
 This tmSecurityName may be later translated from a TLSTM specific
 tmSecurityName to an SNMP engine securityName by the security model.
 A security model, like the TSM security model [RFC5591], may perform
 an identity mapping or a more complex mapping to derive the
 securityName from the tmSecurityName offered by the TLS Transport
 Model.
 The standard View-Based Access Control Model (VACM) access control
 model constrains securityNames to be 32 octets or less in length.  A
 TLSTM generated tmSecurityName, possibly in combination with a
 messaging or security model that increases the length of the
 securityName, might cause the securityName length to exceed 32
 octets.  For example, a 32-octet tmSecurityName derived from an IPv6
 address, paired with a TSM prefix, will generate a 36-octet
 securityName.  Such a securityName will not be able to be used with
 standard VACM or TARGET MIB modules.  Operators should be careful to
 select algorithms and subjectAltNames to avoid this situation.

Hardaker Standards Track [Page 16] RFC 6353 TLS Transport Model for SNMP July 2011

 A pictorial view of the complete transformation process (using the
 TSM security model for the example) is shown below:
  +-------------+     +-------+                   +-----+
  | Certificate |     |       |                   |     |
  |    Path     |     | TLSTM |  tmSecurityName   | TSM |
  | Validation  | --> |       | ----------------->|     |
  +-------------+     +-------+                   +-----+
                                                      |
                                                      | securityName
                                                      V
                                                  +-------------+
                                                  | application |
                                                  +-------------+

4.2. (D)TLS Usage

 (D)TLS MUST negotiate a cipher_suite that uses X.509 certificates for
 authentication, and MUST authenticate both the client and the server.
 The mandatory-to-implement cipher_suite is specified in the TLS
 specification [RFC5246].
 TLSTM verifies the certificates when the connection is opened (see
 Section 5.3).  For this reason, TLS renegotiation with different
 certificates MUST NOT be done.  That is, implementations MUST either
 disable renegotiation completely (RECOMMENDED), or they MUST present
 the same certificate during renegotiation (and MUST verify that the
 other end presented the same certificate).
 For DTLS over UDP, each SNMP message MUST be placed in a single UDP
 datagram; it MAY be split to multiple DTLS records.  In other words,
 if a single datagram contains multiple DTLS application_data records,
 they are concatenated when received.  The TLSTM implementation SHOULD
 return an error if the SNMP message does not fit in the UDP datagram,
 and thus cannot be sent.
 For DTLS over UDP, the DTLS server implementation MUST support DTLS
 cookies ([RFC4347] already requires that clients support DTLS
 cookies).  Implementations are not required to perform the cookie
 exchange for every DTLS handshake; however, enabling it by default is
 RECOMMENDED.
 For DTLS, replay protection MUST be used.

Hardaker Standards Track [Page 17] RFC 6353 TLS Transport Model for SNMP July 2011

4.3. SNMP Services

 This section describes the services provided by the TLS Transport
 Model with their inputs and outputs.  The services are between the
 Transport Model and the Dispatcher.
 The services are described as primitives of an abstract service
 interface (ASI) and the inputs and outputs are described as abstract
 data elements as they are passed in these abstract service
 primitives.

4.3.1. SNMP Services for an Outgoing Message

 The Dispatcher passes the information to the TLS Transport Model
 using the ASI defined in the Transport Subsystem:
    statusInformation =
    sendMessage(
    IN   destTransportDomain           -- transport domain to be used
    IN   destTransportAddress          -- transport address to be used
    IN   outgoingMessage               -- the message to send
    IN   outgoingMessageLength         -- its length
    IN   tmStateReference              -- reference to transport state
     )
 The abstract data elements returned from or passed as parameters into
 the abstract service primitives are as follows:
 statusInformation:  An indication of whether the sending of the
    message was successful.  If not, it is an indication of the
    problem.
 destTransportDomain:  The transport domain for the associated
    destTransportAddress.  The Transport Model uses this parameter to
    determine the transport type of the associated
    destTransportAddress.  This document specifies the
    snmpTLSTCPDomain and the snmpDTLSUDPDomain transport domains.
 destTransportAddress:  The transport address of the destination TLS
    Transport Model in a format specified by the SnmpTLSAddress
    TEXTUAL-CONVENTION.
 outgoingMessage:  The outgoing message to send to (D)TLS for
    encapsulation and transmission.
 outgoingMessageLength:  The length of the outgoingMessage.

Hardaker Standards Track [Page 18] RFC 6353 TLS Transport Model for SNMP July 2011

 tmStateReference:  A reference used to pass model-specific and
    mechanism-specific parameters between the Transport Subsystem and
    transport-aware Security Models.

4.3.2. SNMP Services for an Incoming Message

 The TLS Transport Model processes the received message from the
 network using the (D)TLS service and then passes it to the Dispatcher
 using the following ASI:
    statusInformation =
    receiveMessage(
    IN   transportDomain               -- origin transport domain
    IN   transportAddress              -- origin transport address
    IN   incomingMessage               -- the message received
    IN   incomingMessageLength         -- its length
    IN   tmStateReference              -- reference to transport state
     )
 The abstract data elements returned from or passed as parameters into
 the abstract service primitives are as follows:
 statusInformation:  An indication of whether the passing of the
    message was successful.  If not, it is an indication of the
    problem.
 transportDomain:  The transport domain for the associated
    transportAddress.  This document specifies the snmpTLSTCPDomain
    and the snmpDTLSUDPDomain transport domains.
 transportAddress:  The transport address of the source of the
    received message in a format specified by the SnmpTLSAddress
    TEXTUAL-CONVENTION.
 incomingMessage:  The whole SNMP message after being processed by
    (D)TLS.
 incomingMessageLength:  The length of the incomingMessage.
 tmStateReference:  A reference used to pass model-specific and
    mechanism-specific parameters between the Transport Subsystem and
    transport-aware Security Models.

Hardaker Standards Track [Page 19] RFC 6353 TLS Transport Model for SNMP July 2011

4.4. Cached Information and References

 When performing SNMP processing, there are two levels of state
 information that may need to be retained: the immediate state linking
 a request-response pair, and potentially longer-term state relating
 to transport and security.  "Transport Subsystem for the Simple
 Network Management Protocol (SNMP)" [RFC5590] defines general
 requirements for caches and references.

4.4.1. TLS Transport Model Cached Information

 The TLS Transport Model has specific responsibilities regarding the
 cached information.  See the Elements of Procedure in Section 5 for
 detailed processing instructions on the use of the tmStateReference
 fields by the TLS Transport Model.

4.4.1.1. tmSecurityName

 The tmSecurityName MUST be a human-readable name (in snmpAdminString
 format) representing the identity that has been set according to the
 procedures in Section 5.  The tmSecurityName MUST be constant for all
 traffic passing through a single TLSTM session.  Messages MUST NOT be
 sent through an existing (D)TLS connection that was established using
 a different tmSecurityName.
 On the (D)TLS server side of a connection, the tmSecurityName is
 derived using the procedures described in Section 5.3.2 and the SNMP-
 TLS-TM-MIB's snmpTlstmCertToTSNTable DESCRIPTION clause.
 On the (D)TLS client side of a connection, the tmSecurityName is
 presented to the TLS Transport Model by the security model through
 the tmStateReference.  This tmSecurityName is typically a copy of or
 is derived from the securityName that was passed by application
 (possibly because of configuration specified in the SNMP-TARGET-MIB).
 The Security Model likely derived the tmSecurityName from the
 securityName presented to the Security Model by the application
 (possibly because of configuration specified in the SNMP-TARGET-MIB).
 Transport-Model-aware security models derive tmSecurityName from a
 securityName, possibly configured in MIB modules for notifications
 and access controls.  Transport Models SHOULD use predictable
 tmSecurityNames so operators will know what to use when configuring
 MIB modules that use securityNames derived from tmSecurityNames.  The
 TLSTM generates predictable tmSecurityNames based on the
 configuration found in the SNMP-TLS-TM-MIB's snmpTlstmCertToTSNTable
 and relies on the network operators to have configured this table
 appropriately.

Hardaker Standards Track [Page 20] RFC 6353 TLS Transport Model for SNMP July 2011

4.4.1.2. tmSessionID

 The tmSessionID MUST be recorded per message at the time of receipt.
 When tmSameSecurity is set, the recorded tmSessionID can be used to
 determine whether the (D)TLS connection available for sending a
 corresponding outgoing message is the same (D)TLS connection as was
 used when receiving the incoming message (e.g., a response to a
 request).

4.4.1.3. Session State

 The per-session state that is referenced by tmStateReference may be
 saved across multiple messages in a Local Configuration Datastore.
 Additional session/connection state information might also be stored
 in a Local Configuration Datastore.

5. Elements of Procedure

 Abstract service interfaces have been defined by [RFC3411] and
 further augmented by [RFC5590] to describe the conceptual data flows
 between the various subsystems within an SNMP entity.  The TLSTM uses
 some of these conceptual data flows when communicating between
 subsystems.
 To simplify the elements of procedure, the release of state
 information is not always explicitly specified.  As a general rule,
 if state information is available when a message gets discarded, the
 message-state information should also be released.  If state
 information is available when a session is closed, the session state
 information should also be released.  Sensitive information, like
 cryptographic keys, should be overwritten appropriately prior to
 being released.
 An error indication in statusInformation will typically include the
 Object Identifier (OID) and value for an incremented error counter.
 This may be accompanied by the requested securityLevel and the
 tmStateReference.  Per-message context information is not accessible
 to Transport Models, so for the returned counter OID and value,
 contextEngine would be set to the local value of snmpEngineID and
 contextName to the default context for error counters.

5.1. Procedures for an Incoming Message

 This section describes the procedures followed by the (D)TLS
 Transport Model when it receives a (D)TLS protected packet.  The
 required functionality is broken into two different sections.

Hardaker Standards Track [Page 21] RFC 6353 TLS Transport Model for SNMP July 2011

 Section 5.1.1 describes the processing required for de-multiplexing
 multiple DTLS connections, which is specifically needed for DTLS over
 UDP sessions.  It is assumed that TLS protocol implementations
 already provide appropriate message demultiplexing.
 Section 5.1.2 describes the transport processing required once the
 (D)TLS processing has been completed.  This will be needed for all
 (D)TLS-based connections.

5.1.1. DTLS over UDP Processing for Incoming Messages

 Demultiplexing of incoming packets into separate DTLS sessions MUST
 be implemented.  For connection-oriented transport protocols, such as
 TCP, the transport protocol takes care of demultiplexing incoming
 packets to the right connection.  For DTLS over UDP, this
 demultiplexing will either need to be done within the DTLS
 implementation, if supported, or by the TLSTM implementation.
 Like TCP, DTLS over UDP uses the four-tuple <source IP, destination
 IP, source port, destination port> for identifying the connection
 (and relevant DTLS connection state).  This means that when
 establishing a new session, implementations MUST use a different UDP
 source port number for each active connection to a remote destination
 IP-address/port-number combination to ensure the remote entity can
 disambiguate between multiple connections.
 If demultiplexing received UDP datagrams to DTLS connection state is
 done by the TLSTM implementation (instead of the DTLS
 implementation), the steps below describe one possible method to
 accomplish this.
 The important output results from the steps in this process are the
 remote transport address, incomingMessage, incomingMessageLength, and
 the tlstmSessionID.
 1)  The TLS Transport Model examines the raw UDP message, in an
     implementation-dependent manner.
 2)  The TLS Transport Model queries the Local Configuration Datastore
     (LCD) (see [RFC3411], Section 3.4.2) using the transport
     parameters (source and destination IP addresses and ports) to
     determine if a session already exists.
     2a)  If a matching entry in the LCD does not exist, then the UDP
          packet is passed to the DTLS implementation for processing.
          If the DTLS implementation decides to continue with the
          connection and allocate state for it, it returns a new DTLS
          connection handle (an implementation dependent detail).  In

Hardaker Standards Track [Page 22] RFC 6353 TLS Transport Model for SNMP July 2011

          this case, TLSTM selects a new tlstmSessionId, and caches
          this and the DTLS connection handle as a new entry in the
          LCD (indexed by the transport parameters).  If the DTLS
          implementation returns an error or does not allocate
          connection state (which can happen with the stateless cookie
          exchange), processing stops.
     2b)  If a session does exist in the LCD, then its DTLS connection
          handle (an implementation dependent detail) and its
          tlstmSessionId is extracted from the LCD.  The UDP packet
          and the connection handle are passed to the DTLS
          implementation.  If the DTLS implementation returns success
          but does not return an incomingMessage and an
          incomingMessageLength, then processing stops (this is the
          case when the UDP datagram contained DTLS handshake
          messages, for example).  If the DTLS implementation returns
          an error, then processing stops.
 3)  Retrieve the incomingMessage and an incomingMessageLength from
     DTLS.  These results and the tlstmSessionID are used below in
     Section 5.1.2 to complete the processing of the incoming message.

5.1.2. Transport Processing for Incoming SNMP Messages

 The procedures in this section describe how the TLS Transport Model
 should process messages that have already been properly extracted
 from the (D)TLS stream.  Note that care must be taken when processing
 messages originating from either TLS or DTLS to ensure they're
 complete and single.  For example, multiple SNMP messages can be
 passed through a single DTLS message and partial SNMP messages may be
 received from a TLS stream.  These steps describe the processing of a
 singular SNMP message after it has been delivered from the (D)TLS
 stream.
 1)  Determine the tlstmSessionID for the incoming message.  The
     tlstmSessionID MUST be a unique session identifier for this
     (D)TLS connection.  The contents and format of this identifier
     are implementation dependent as long as it is unique to the
     session.  A session identifier MUST NOT be reused until all
     references to it are no longer in use.  The tmSessionID is equal
     to the tlstmSessionID discussed in Section 5.1.1. tmSessionID
     refers to the session identifier when stored in the
     tmStateReference and tlstmSessionID refers to the session
     identifier when stored in the LCD.  They MUST always be equal
     when processing a given session's traffic.

Hardaker Standards Track [Page 23] RFC 6353 TLS Transport Model for SNMP July 2011

     If this is the first message received through this session, and
     the session does not have an assigned tlstmSessionID yet, then
     the snmpTlstmSessionAccepts counter is incremented and a
     tlstmSessionID for the session is created.  This will only happen
     on the server side of a connection because a client would have
     already assigned a tlstmSessionID during the openSession()
     invocation.  Implementations may have performed the procedures
     described in Section 5.3.2 prior to this point or they may
     perform them now, but the procedures described in Section 5.3.2
     MUST be performed before continuing beyond this point.
 2)  Create a tmStateReference cache for the subsequent reference and
     assign the following values within it:
     tmTransportDomain  = snmpTLSTCPDomain or snmpDTLSUDPDomain as
        appropriate.
     tmTransportAddress  = The address from which the message
        originated.
     tmSecurityLevel  = The derived tmSecurityLevel for the session,
        as discussed in Sections 3.1.2 and 5.3.
     tmSecurityName  = The derived tmSecurityName for the session as
        discussed in Section 5.3.  This value MUST be constant during
        the lifetime of the session.
     tmSessionID  = The tlstmSessionID described in step 1 above.
 3)  The incomingMessage and incomingMessageLength are assigned values
     from the (D)TLS processing.
 4)  The TLS Transport Model passes the transportDomain,
     transportAddress, incomingMessage, and incomingMessageLength to
     the Dispatcher using the receiveMessage ASI:
    statusInformation =
    receiveMessage(
    IN   transportDomain     -- snmpTLSTCPDomain or snmpDTLSUDPDomain,
    IN   transportAddress    -- address for the received message
    IN   incomingMessage        -- the whole SNMP message from (D)TLS
    IN   incomingMessageLength  -- the length of the SNMP message
    IN   tmStateReference    -- transport info
     )

Hardaker Standards Track [Page 24] RFC 6353 TLS Transport Model for SNMP July 2011

5.2. Procedures for an Outgoing SNMP Message

 The Dispatcher sends a message to the TLS Transport Model using the
 following ASI:
    statusInformation =
    sendMessage(
    IN   destTransportDomain           -- transport domain to be used
    IN   destTransportAddress          -- transport address to be used
    IN   outgoingMessage               -- the message to send
    IN   outgoingMessageLength         -- its length
    IN   tmStateReference              -- transport info
    )
 This section describes the procedure followed by the TLS Transport
 Model whenever it is requested through this ASI to send a message.
 1)  If tmStateReference does not refer to a cache containing values
     for tmTransportDomain, tmTransportAddress, tmSecurityName,
     tmRequestedSecurityLevel, and tmSameSecurity, then increment the
     snmpTlstmSessionInvalidCaches counter, discard the message, and
     return the error indication in the statusInformation.  Processing
     of this message stops.
 2)  Extract the tmSessionID, tmTransportDomain, tmTransportAddress,
     tmSecurityName, tmRequestedSecurityLevel, and tmSameSecurity
     values from the tmStateReference.  Note: the tmSessionID value
     may be undefined if no session exists yet over which the message
     can be sent.
 3)  If tmSameSecurity is true and tmSessionID is either undefined or
     refers to a session that is no longer open, then increment the
     snmpTlstmSessionNoSessions counter, discard the message, and
     return the error indication in the statusInformation.  Processing
     of this message stops.
 4)  If tmSameSecurity is false and tmSessionID refers to a session
     that is no longer available, then an implementation SHOULD open a
     new session, using the openSession() ASI (described in greater
     detail in step 5b).  Instead of opening a new session an
     implementation MAY return an snmpTlstmSessionNoSessions error to
     the calling module and stop the processing of the message.
 5)  If tmSessionID is undefined, then use tmTransportDomain,
     tmTransportAddress, tmSecurityName, and tmRequestedSecurityLevel
     to see if there is a corresponding entry in the LCD suitable to
     send the message over.

Hardaker Standards Track [Page 25] RFC 6353 TLS Transport Model for SNMP July 2011

     5a)  If there is a corresponding LCD entry, then this session
          will be used to send the message.
     5b)  If there is no corresponding LCD entry, then open a session
          using the openSession() ASI (discussed further in
          Section 5.3.1).  Implementations MAY wish to offer message
          buffering to prevent redundant openSession() calls for the
          same cache entry.  If an error is returned from
          openSession(), then discard the message, discard the
          tmStateReference, increment the snmpTlstmSessionOpenErrors,
          return an error indication to the calling module, and stop
          the processing of the message.
 6)  Using either the session indicated by the tmSessionID (if there
     was one) or the session resulting from a previous step (4 or 5),
     pass the outgoingMessage to (D)TLS for encapsulation and
     transmission.

5.3. Establishing or Accepting a Session

 Establishing a (D)TLS connection as either a client or a server
 requires slightly different processing.  The following two sections
 describe the necessary processing steps.

5.3.1. Establishing a Session as a Client

 The TLS Transport Model provides the following primitive for use by a
 client to establish a new (D)TLS connection:
 statusInformation =           -- errorIndication or success
 openSession(
 IN   tmStateReference         -- transport information to be used
 OUT  tmStateReference         -- transport information to be used
 IN   maxMessageSize           -- of the sending SNMP entity
 )
 The following describes the procedure to follow when establishing an
 SNMP over a (D)TLS connection between SNMP engines for exchanging
 SNMP messages.  This process is followed by any SNMP client's engine
 when establishing a session for subsequent use.
 This procedure MAY be done automatically for an SNMP application that
 initiates a transaction, such as a command generator, a notification
 originator, or a proxy forwarder.
 1)  The snmpTlstmSessionOpens counter is incremented.

Hardaker Standards Track [Page 26] RFC 6353 TLS Transport Model for SNMP July 2011

 2)  The client selects the appropriate certificate and cipher_suites
     for the key agreement based on the tmSecurityName and the
     tmRequestedSecurityLevel for the session.  For sessions being
     established as a result of an SNMP-TARGET-MIB based operation,
     the certificate will potentially have been identified via the
     snmpTlstmParamsTable mapping and the cipher_suites will have to
     be taken from a system-wide or implementation-specific
     configuration.  If no row in the snmpTlstmParamsTable exists,
     then implementations MAY choose to establish the connection using
     a default client certificate available to the application.
     Otherwise, the certificate and appropriate cipher_suites will
     need to be passed to the openSession() ASI as supplemental
     information or configured through an implementation-dependent
     mechanism.  It is also implementation-dependent and possibly
     policy-dependent how tmRequestedSecurityLevel will be used to
     influence the security capabilities provided by the (D)TLS
     connection.  However this is done, the security capabilities
     provided by (D)TLS MUST be at least as high as the level of
     security indicated by the tmRequestedSecurityLevel parameter.
     The actual security level of the session is reported in the
     tmStateReference cache as tmSecurityLevel.  For (D)TLS to provide
     strong authentication, each principal acting as a command
     generator SHOULD have its own certificate.
 3)  Using the destTransportDomain and destTransportAddress values,
     the client will initiate the (D)TLS handshake protocol to
     establish session keys for message integrity and encryption.
     If the attempt to establish a session is unsuccessful, then
     snmpTlstmSessionOpenErrors is incremented, an error indication is
     returned, and processing stops.  If the session failed to open
     because the presented server certificate was unknown or invalid,
     then the snmpTlstmSessionUnknownServerCertificate or
     snmpTlstmSessionInvalidServerCertificates MUST be incremented and
     an snmpTlstmServerCertificateUnknown or
     snmpTlstmServerInvalidCertificate notification SHOULD be sent as
     appropriate.  Reasons for server certificate invalidation
     include, but are not limited to, cryptographic validation
     failures and an unexpected presented certificate identity.
 4)  The (D)TLS client MUST then verify that the (D)TLS server's
     presented certificate is the expected certificate.  The (D)TLS
     client MUST NOT transmit SNMP messages until the server
     certificate has been authenticated, the client certificate has
     been transmitted, and the TLS connection has been fully
     established.

Hardaker Standards Track [Page 27] RFC 6353 TLS Transport Model for SNMP July 2011

     If the connection is being established from a configuration based
     on SNMP-TARGET-MIB configuration, then the snmpTlstmAddrTable
     DESCRIPTION clause describes how the verification is done (using
     either a certificate fingerprint, or an identity authenticated
     via certification path validation).
     If the connection is being established for reasons other than
     configuration found in the SNMP-TARGET-MIB, then configuration
     and procedures outside the scope of this document should be
     followed.  Configuration mechanisms SHOULD be similar in nature
     to those defined in the snmpTlstmAddrTable to ensure consistency
     across management configuration systems.  For example, a command-
     line tool for generating SNMP GETs might support specifying
     either the server's certificate fingerprint or the expected host
     name as a command-line argument.
 5)  (D)TLS provides assurance that the authenticated identity has
     been signed by a trusted configured Certification Authority.  If
     verification of the server's certificate fails in any way (for
     example, because of failures in cryptographic verification or the
     presented identity did not match the expected named entity), then
     the session establishment MUST fail, and the
     snmpTlstmSessionInvalidServerCertificates object is incremented.
     If the session cannot be opened for any reason at all, including
     cryptographic verification failures and snmpTlstmCertToTSNTable
     lookup failures, then the snmpTlstmSessionOpenErrors counter is
     incremented and processing stops.
 6)  The TLSTM-specific session identifier (tlstmSessionID) is set in
     the tmSessionID of the tmStateReference passed to the TLS
     Transport Model to indicate that the session has been established
     successfully and to point to a specific (D)TLS connection for
     future use.  The tlstmSessionID is also stored in the LCD for
     later lookup during processing of incoming messages
     (Section 5.1.2).

5.3.2. Accepting a Session as a Server

 A (D)TLS server should accept new session connections from any client
 for which it is able to verify the client's credentials.  This is
 done by authenticating the client's presented certificate through a
 certificate path validation process (e.g., [RFC5280]) or through
 certificate fingerprint verification using fingerprints configured in
 the snmpTlstmCertToTSNTable.  Afterward, the server will determine
 the identity of the remote entity using the following procedures.

Hardaker Standards Track [Page 28] RFC 6353 TLS Transport Model for SNMP July 2011

 The (D)TLS server identifies the authenticated identity from the
 (D)TLS client's principal certificate using configuration information
 from the snmpTlstmCertToTSNTable mapping table.  The (D)TLS server
 MUST request and expect a certificate from the client and MUST NOT
 accept SNMP messages over the (D)TLS connection until the client has
 sent a certificate and it has been authenticated.  The resulting
 derived tmSecurityName is recorded in the tmStateReference cache as
 tmSecurityName.  The details of the lookup process are fully
 described in the DESCRIPTION clause of the snmpTlstmCertToTSNTable
 MIB object.  If any verification fails in any way (for example,
 because of failures in cryptographic verification or because of the
 lack of an appropriate row in the snmpTlstmCertToTSNTable), then the
 session establishment MUST fail, and the
 snmpTlstmSessionInvalidClientCertificates object is incremented.  If
 the session cannot be opened for any reason at all, including
 cryptographic verification failures, then the
 snmpTlstmSessionOpenErrors counter is incremented and processing
 stops.
 Servers that wish to support multiple principals at a particular port
 SHOULD make use of a (D)TLS extension that allows server-side
 principal selection like the Server Name Indication extension defined
 in Section 3.1 of [RFC4366].  Supporting this will allow, for
 example, sending notifications to a specific principal at a given TCP
 or UDP port.

5.4. Closing a Session

 The TLS Transport Model provides the following primitive to close a
 session:
 statusInformation =
 closeSession(
 IN  tmSessionID        -- session ID of the session to be closed
 )
 The following describes the procedure to follow to close a session
 between a client and server.  This process is followed by any SNMP
 engine closing the corresponding SNMP session.
 1)  Increment either the snmpTlstmSessionClientCloses or the
     snmpTlstmSessionServerCloses counter as appropriate.
 2)  Look up the session using the tmSessionID.
 3)  If there is no open session associated with the tmSessionID, then
     closeSession processing is completed.

Hardaker Standards Track [Page 29] RFC 6353 TLS Transport Model for SNMP July 2011

 4)  Have (D)TLS close the specified connection.  This MUST include
     sending a close_notify TLS Alert to inform the other side that
     session cleanup may be performed.

6. MIB Module Overview

 This MIB module provides management of the TLS Transport Model.  It
 defines needed textual conventions, statistical counters,
 notifications, and configuration infrastructure necessary for session
 establishment.  Example usage of the configuration tables can be
 found in Appendix A.

6.1. Structure of the MIB Module

 Objects in this MIB module are arranged into subtrees.  Each subtree
 is organized as a set of related objects.  The overall structure and
 assignment of objects to their subtrees, and the intended purpose of
 each subtree, is shown below.

6.2. Textual Conventions

 Generic and Common Textual Conventions used in this module can be
 found summarized at http://www.ops.ietf.org/mib-common-tcs.html.
 This module defines the following new Textual Conventions:
 o  A new TransportAddress format for describing (D)TLS connection
    addressing requirements.
 o  A certificate fingerprint allowing MIB module objects to
    generically refer to a stored X.509 certificate using a
    cryptographic hash as a reference pointer.

6.3. Statistical Counters

 The SNMP-TLS-TM-MIB defines counters that provide network management
 stations with information about session usage and potential errors
 that a device may be experiencing.

6.4. Configuration Tables

 The SNMP-TLS-TM-MIB defines configuration tables that an
 administrator can use for configuring a device for sending and
 receiving SNMP messages over (D)TLS.  In particular, there are MIB
 tables that extend the SNMP-TARGET-MIB for configuring (D)TLS
 certificate usage and a MIB table for mapping incoming (D)TLS client
 certificates to SNMPv3 tmSecurityNames.

Hardaker Standards Track [Page 30] RFC 6353 TLS Transport Model for SNMP July 2011

6.4.1. Notifications

 The SNMP-TLS-TM-MIB defines notifications to alert management
 stations when a (D)TLS connection fails because a server's presented
 certificate did not meet an expected value
 (snmpTlstmServerCertificateUnknown) or because cryptographic
 validation failed (snmpTlstmServerInvalidCertificate).

6.5. Relationship to Other MIB Modules

 Some management objects defined in other MIB modules are applicable
 to an entity implementing the TLS Transport Model.  In particular, it
 is assumed that an entity implementing the SNMP-TLS-TM-MIB will
 implement the SNMPv2-MIB [RFC3418], the SNMP-FRAMEWORK-MIB [RFC3411],
 the SNMP-TARGET-MIB [RFC3413], the SNMP-NOTIFICATION-MIB [RFC3413],
 and the SNMP-VIEW-BASED-ACM-MIB [RFC3415].
 The SNMP-TLS-TM-MIB module contained in this document is for managing
 TLS Transport Model information.

6.5.1. MIB Modules Required for IMPORTS

 The SNMP-TLS-TM-MIB module imports items from SNMPv2-SMI [RFC2578],
 SNMPv2-TC [RFC2579], SNMP-FRAMEWORK-MIB [RFC3411], SNMP-TARGET-MIB
 [RFC3413], and SNMPv2-CONF [RFC2580].

7. MIB Module Definition

SNMP-TLS-TM-MIB DEFINITIONS ::= BEGIN

IMPORTS

  MODULE-IDENTITY, OBJECT-TYPE,
  OBJECT-IDENTITY, mib-2, snmpDomains,
  Counter32, Unsigned32, Gauge32, NOTIFICATION-TYPE
    FROM SNMPv2-SMI                 -- RFC 2578 or any update thereof
  TEXTUAL-CONVENTION, TimeStamp, RowStatus, StorageType,
  AutonomousType
    FROM SNMPv2-TC                  -- RFC 2579 or any update thereof
  MODULE-COMPLIANCE, OBJECT-GROUP, NOTIFICATION-GROUP
    FROM SNMPv2-CONF                -- RFC 2580 or any update thereof
  SnmpAdminString
    FROM SNMP-FRAMEWORK-MIB         -- RFC 3411 or any update thereof
  snmpTargetParamsName, snmpTargetAddrName
    FROM SNMP-TARGET-MIB            -- RFC 3413 or any update thereof
  ;

snmpTlstmMIB MODULE-IDENTITY

  LAST-UPDATED "201107190000Z"

Hardaker Standards Track [Page 31] RFC 6353 TLS Transport Model for SNMP July 2011

  ORGANIZATION "ISMS Working Group"
  CONTACT-INFO "WG-EMail:   isms@lists.ietf.org
                Subscribe:  isms-request@lists.ietf.org
                Chairs:
                   Juergen Schoenwaelder
                   Jacobs University Bremen
                   Campus Ring 1
                   28725 Bremen
                   Germany
                   +49 421 200-3587
                   j.schoenwaelder@jacobs-university.de
                   Russ Mundy
                   SPARTA, Inc.
                   7110 Samuel Morse Drive
                   Columbia, MD  21046
                   USA
                Editor:
                   Wes Hardaker
                   SPARTA, Inc.
                   P.O. Box 382
                   Davis, CA  95617
                   USA
                   ietf@hardakers.net
                "
  DESCRIPTION  "
      The TLS Transport Model MIB
      Copyright (c) 2010-2011 IETF Trust and the persons identified
      as authors of the code.  All rights reserved.
      Redistribution and use in source and binary forms, with or
      without modification, is permitted pursuant to, and subject
      to the license terms contained in, the Simplified BSD License
      set forth in Section 4.c of the IETF Trust's Legal Provisions
      Relating to IETF Documents
      (http://trustee.ietf.org/license-info)."
     REVISION     "201107190000Z"
     DESCRIPTION  "This version of this MIB module is part of
                   RFC 6353; see the RFC itself for full legal
                   notices.  The only change was to introduce
                   new wording to reflect require changes for
                   IDNA addresses in the SnmpTLSAddress TC."

Hardaker Standards Track [Page 32] RFC 6353 TLS Transport Model for SNMP July 2011

     REVISION     "201005070000Z"
     DESCRIPTION  "This version of this MIB module is part of
                   RFC 5953; see the RFC itself for full legal
                   notices."
  ::= { mib-2 198 }

– subtrees of the SNMP-TLS-TM-MIB –

snmpTlstmNotifications OBJECT IDENTIFIER ::= { snmpTlstmMIB 0 } snmpTlstmIdentities OBJECT IDENTIFIER ::= { snmpTlstmMIB 1 } snmpTlstmObjects OBJECT IDENTIFIER ::= { snmpTlstmMIB 2 } snmpTlstmConformance OBJECT IDENTIFIER ::= { snmpTlstmMIB 3 }

– snmpTlstmObjects - Objects –

snmpTLSTCPDomain OBJECT-IDENTITY

  STATUS      current
  DESCRIPTION
      "The SNMP over TLS via TCP transport domain.  The
      corresponding transport address is of type SnmpTLSAddress.
      The securityName prefix to be associated with the
      snmpTLSTCPDomain is 'tls'.  This prefix may be used by
      security models or other components to identify which secure
      transport infrastructure authenticated a securityName."
  REFERENCE
    "RFC 2579: Textual Conventions for SMIv2"
  ::= { snmpDomains 8 }

snmpDTLSUDPDomain OBJECT-IDENTITY

  STATUS      current
  DESCRIPTION
      "The SNMP over DTLS via UDP transport domain.  The
      corresponding transport address is of type SnmpTLSAddress.
      The securityName prefix to be associated with the
      snmpDTLSUDPDomain is 'dtls'.  This prefix may be used by
      security models or other components to identify which secure
      transport infrastructure authenticated a securityName."
  REFERENCE
    "RFC 2579: Textual Conventions for SMIv2"
  ::= { snmpDomains 9 }

Hardaker Standards Track [Page 33] RFC 6353 TLS Transport Model for SNMP July 2011

SnmpTLSAddress ::= TEXTUAL-CONVENTION

  DISPLAY-HINT "1a"
  STATUS       current
  DESCRIPTION
      "Represents an IPv4 address, an IPv6 address, or a
       US-ASCII-encoded hostname and port number.
      An IPv4 address must be in dotted decimal format followed by a
      colon ':' (US-ASCII character 0x3A) and a decimal port number
      in US-ASCII.
      An IPv6 address must be a colon-separated format (as described
      in RFC 5952), surrounded by square brackets ('[', US-ASCII
      character 0x5B, and ']', US-ASCII character 0x5D), followed by
      a colon ':' (US-ASCII character 0x3A) and a decimal port number
      in US-ASCII.
      A hostname is always in US-ASCII (as per RFC 1123);
      internationalized hostnames are encoded as A-labels as specified
      in  RFC 5890.  The hostname is followed by a
      colon ':' (US-ASCII character 0x3A) and a decimal port number
      in US-ASCII.  The name SHOULD be fully qualified whenever
      possible.
      Values of this textual convention may not be directly usable
      as transport-layer addressing information, and may require
      run-time resolution.  As such, applications that write them
      must be prepared for handling errors if such values are not
      supported, or cannot be resolved (if resolution occurs at the
      time of the management operation).
      The DESCRIPTION clause of TransportAddress objects that may
      have SnmpTLSAddress values must fully describe how (and
      when) such names are to be resolved to IP addresses and vice
      versa.
      This textual convention SHOULD NOT be used directly in object
      definitions since it restricts addresses to a specific
      format.  However, if it is used, it MAY be used either on its
      own or in conjunction with TransportAddressType or
      TransportDomain as a pair.
      When this textual convention is used as a syntax of an index
      object, there may be issues with the limit of 128
      sub-identifiers specified in SMIv2 (STD 58).  It is RECOMMENDED
      that all MIB documents using this textual convention make
      explicit any limitations on index component lengths that
      management software must observe.  This may be done either by

Hardaker Standards Track [Page 34] RFC 6353 TLS Transport Model for SNMP July 2011

      including SIZE constraints on the index components or by
      specifying applicable constraints in the conceptual row
      DESCRIPTION clause or in the surrounding documentation."
  REFERENCE
    "RFC 1123: Requirements for Internet Hosts - Application and
               Support
     RFC 5890: Internationalized Domain Names for Applications (IDNA):
               Definitions and Document Framework
     RFC 5952: A Recommendation for IPv6 Address Text Representation
    "
  SYNTAX       OCTET STRING (SIZE (1..255))

SnmpTLSFingerprint ::= TEXTUAL-CONVENTION

  DISPLAY-HINT "1x:1x"
  STATUS       current
  DESCRIPTION
     "A fingerprint value that can be used to uniquely reference
     other data of potentially arbitrary length.
     An SnmpTLSFingerprint value is composed of a 1-octet hashing
     algorithm identifier followed by the fingerprint value.  The
     octet value encoded is taken from the IANA TLS HashAlgorithm
     Registry (RFC 5246).  The remaining octets are filled using the
     results of the hashing algorithm.
     This TEXTUAL-CONVENTION allows for a zero-length (blank)
     SnmpTLSFingerprint value for use in tables where the
     fingerprint value may be optional.  MIB definitions or
     implementations may refuse to accept a zero-length value as
     appropriate."
     REFERENCE "RFC 5246: The Transport Layer
                Security (TLS) Protocol Version 1.2
                http://www.iana.org/assignments/tls-parameters/
     "
  SYNTAX OCTET STRING (SIZE (0..255))

– Identities for use in the snmpTlstmCertToTSNTable

snmpTlstmCertToTSNMIdentities OBJECT IDENTIFIER

  ::= { snmpTlstmIdentities 1 }

snmpTlstmCertSpecified OBJECT-IDENTITY

  STATUS        current
  DESCRIPTION  "Directly specifies the tmSecurityName to be used for
                this certificate.  The value of the tmSecurityName
                to use is specified in the snmpTlstmCertToTSNData
                column.  The snmpTlstmCertToTSNData column must
                contain a non-zero length SnmpAdminString compliant

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                value or the mapping described in this row must be
                considered a failure."
  ::= { snmpTlstmCertToTSNMIdentities 1 }

snmpTlstmCertSANRFC822Name OBJECT-IDENTITY

  STATUS        current
  DESCRIPTION  "Maps a subjectAltName's rfc822Name to a
                tmSecurityName.  The local part of the rfc822Name is
                passed unaltered but the host-part of the name must
                be passed in lowercase.  This mapping results in a
                1:1 correspondence between equivalent subjectAltName
                rfc822Name values and tmSecurityName values except
                that the host-part of the name MUST be passed in
                lowercase.
                Example rfc822Name Field:  FooBar@Example.COM
                is mapped to tmSecurityName: FooBar@example.com."
  ::= { snmpTlstmCertToTSNMIdentities 2 }

snmpTlstmCertSANDNSName OBJECT-IDENTITY

  STATUS        current
  DESCRIPTION  "Maps a subjectAltName's dNSName to a
                tmSecurityName after first converting it to all
                lowercase (RFC 5280 does not specify converting to
                lowercase so this involves an extra step).  This
                mapping results in a 1:1 correspondence between
                subjectAltName dNSName values and the tmSecurityName
                values."
  REFERENCE "RFC 5280 - Internet X.509 Public Key Infrastructure
                       Certificate and Certificate Revocation
                       List (CRL) Profile."
  ::= { snmpTlstmCertToTSNMIdentities 3 }

snmpTlstmCertSANIpAddress OBJECT-IDENTITY

  STATUS        current
  DESCRIPTION  "Maps a subjectAltName's iPAddress to a
                tmSecurityName by transforming the binary encoded
                address as follows:
                1) for IPv4, the value is converted into a
                   decimal-dotted quad address (e.g., '192.0.2.1').
                2) for IPv6 addresses, the value is converted into a
                   32-character all lowercase hexadecimal string
                   without any colon separators.

Hardaker Standards Track [Page 36] RFC 6353 TLS Transport Model for SNMP July 2011

                This mapping results in a 1:1 correspondence between
                subjectAltName iPAddress values and the
                tmSecurityName values.
                The resulting length of an encoded IPv6 address is
                the maximum length supported by the View-Based
                Access Control Model (VACM).  Using both the
                Transport Security Model's support for transport
                prefixes (see the SNMP-TSM-MIB's
                snmpTsmConfigurationUsePrefix object for details)
                will result in securityName lengths that exceed what
                VACM can handle."
  ::= { snmpTlstmCertToTSNMIdentities 4 }

snmpTlstmCertSANAny OBJECT-IDENTITY

  STATUS        current
  DESCRIPTION  "Maps any of the following fields using the
                corresponding mapping algorithms:
                |------------+----------------------------|
                | Type       | Algorithm                  |
                |------------+----------------------------|
                | rfc822Name | snmpTlstmCertSANRFC822Name |
                | dNSName    | snmpTlstmCertSANDNSName    |
                | iPAddress  | snmpTlstmCertSANIpAddress  |
                |------------+----------------------------|
                The first matching subjectAltName value found in the
                certificate of the above types MUST be used when
                deriving the tmSecurityName.  The mapping algorithm
                specified in the 'Algorithm' column MUST be used to
                derive the tmSecurityName.
                This mapping results in a 1:1 correspondence between
                subjectAltName values and tmSecurityName values.  The
                three sub-mapping algorithms produced by this
                combined algorithm cannot produce conflicting
                results between themselves."
  ::= { snmpTlstmCertToTSNMIdentities 5 }

snmpTlstmCertCommonName OBJECT-IDENTITY

  STATUS        current
  DESCRIPTION  "Maps a certificate's CommonName to a tmSecurityName
                after converting it to a UTF-8 encoding.  The usage
                of CommonNames is deprecated and users are
                encouraged to use subjectAltName mapping methods
                instead.  This mapping results in a 1:1

Hardaker Standards Track [Page 37] RFC 6353 TLS Transport Model for SNMP July 2011

                correspondence between certificate CommonName values
                and tmSecurityName values."
  ::= { snmpTlstmCertToTSNMIdentities 6 }

– The snmpTlstmSession Group

snmpTlstmSession OBJECT IDENTIFIER ::= { snmpTlstmObjects 1 }

snmpTlstmSessionOpens OBJECT-TYPE

  SYNTAX       Counter32
  MAX-ACCESS   read-only
  STATUS       current
  DESCRIPTION
     "The number of times an openSession() request has been executed
     as a (D)TLS client, regardless of whether it succeeded or
     failed."
  ::= { snmpTlstmSession 1 }

snmpTlstmSessionClientCloses OBJECT-TYPE

  SYNTAX       Counter32
  MAX-ACCESS   read-only
  STATUS       current
  DESCRIPTION
      "The number of times a closeSession() request has been
      executed as a (D)TLS client, regardless of whether it
      succeeded or failed."
  ::= { snmpTlstmSession 2 }

snmpTlstmSessionOpenErrors OBJECT-TYPE

  SYNTAX       Counter32
  MAX-ACCESS   read-only
  STATUS       current
  DESCRIPTION
      "The number of times an openSession() request failed to open a
      session as a (D)TLS client, for any reason."
  ::= { snmpTlstmSession 3 }

snmpTlstmSessionAccepts OBJECT-TYPE

  SYNTAX       Counter32
  MAX-ACCESS   read-only
  STATUS       current
  DESCRIPTION
     "The number of times a (D)TLS server has accepted a new
     connection from a client and has received at least one SNMP
     message through it."
  ::= { snmpTlstmSession 4 }

Hardaker Standards Track [Page 38] RFC 6353 TLS Transport Model for SNMP July 2011

snmpTlstmSessionServerCloses OBJECT-TYPE

  SYNTAX       Counter32
  MAX-ACCESS   read-only
  STATUS       current
  DESCRIPTION
      "The number of times a closeSession() request has been
      executed as a (D)TLS server, regardless of whether it
      succeeded or failed."
  ::= { snmpTlstmSession 5 }

snmpTlstmSessionNoSessions OBJECT-TYPE

  SYNTAX       Counter32
  MAX-ACCESS   read-only
  STATUS       current
  DESCRIPTION
      "The number of times an outgoing message was dropped because
      the session associated with the passed tmStateReference was no
      longer (or was never) available."
  ::= { snmpTlstmSession 6 }

snmpTlstmSessionInvalidClientCertificates OBJECT-TYPE

  SYNTAX       Counter32
  MAX-ACCESS   read-only
  STATUS       current
  DESCRIPTION
      "The number of times an incoming session was not established
      on a (D)TLS server because the presented client certificate
      was invalid.  Reasons for invalidation include, but are not
      limited to, cryptographic validation failures or lack of a
      suitable mapping row in the snmpTlstmCertToTSNTable."
  ::= { snmpTlstmSession 7 }

snmpTlstmSessionUnknownServerCertificate OBJECT-TYPE

  SYNTAX       Counter32
  MAX-ACCESS   read-only
  STATUS       current
  DESCRIPTION
      "The number of times an outgoing session was not established
       on a (D)TLS client because the server certificate presented
       by an SNMP over (D)TLS server was invalid because no
       configured fingerprint or Certification Authority (CA) was
       acceptable to validate it.
       This may result because there was no entry in the
       snmpTlstmAddrTable or because no path could be found to a
       known CA."
  ::= { snmpTlstmSession 8 }

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snmpTlstmSessionInvalidServerCertificates OBJECT-TYPE

  SYNTAX       Counter32
  MAX-ACCESS   read-only
  STATUS       current
  DESCRIPTION
      "The number of times an outgoing session was not established
       on a (D)TLS client because the server certificate presented
       by an SNMP over (D)TLS server could not be validated even if
       the fingerprint or expected validation path was known.  That
       is, a cryptographic validation error occurred during
       certificate validation processing.
      Reasons for invalidation include, but are not
      limited to, cryptographic validation failures."
  ::= { snmpTlstmSession 9 }

snmpTlstmSessionInvalidCaches OBJECT-TYPE

  SYNTAX       Counter32
  MAX-ACCESS   read-only
  STATUS       current
  DESCRIPTION
      "The number of outgoing messages dropped because the
      tmStateReference referred to an invalid cache."
  ::= { snmpTlstmSession 10 }

– Configuration Objects

snmpTlstmConfig OBJECT IDENTIFIER ::= { snmpTlstmObjects 2 }

– Certificate mapping

snmpTlstmCertificateMapping OBJECT IDENTIFIER ::= { snmpTlstmConfig 1 }

snmpTlstmCertToTSNCount OBJECT-TYPE

  SYNTAX      Gauge32
  MAX-ACCESS  read-only
  STATUS      current
  DESCRIPTION
      "A count of the number of entries in the
      snmpTlstmCertToTSNTable."
  ::= { snmpTlstmCertificateMapping 1 }

snmpTlstmCertToTSNTableLastChanged OBJECT-TYPE

  SYNTAX      TimeStamp
  MAX-ACCESS  read-only
  STATUS      current

Hardaker Standards Track [Page 40] RFC 6353 TLS Transport Model for SNMP July 2011

  DESCRIPTION
      "The value of sysUpTime.0 when the snmpTlstmCertToTSNTable was
      last modified through any means, or 0 if it has not been
      modified since the command responder was started."
  ::= { snmpTlstmCertificateMapping 2 }

snmpTlstmCertToTSNTable OBJECT-TYPE

  SYNTAX      SEQUENCE OF SnmpTlstmCertToTSNEntry
  MAX-ACCESS  not-accessible
  STATUS      current
  DESCRIPTION
      "This table is used by a (D)TLS server to map the (D)TLS
      client's presented X.509 certificate to a tmSecurityName.
      On an incoming (D)TLS/SNMP connection, the client's presented
      certificate must either be validated based on an established
      trust anchor, or it must directly match a fingerprint in this
      table.  This table does not provide any mechanisms for
      configuring the trust anchors; the transfer of any needed
      trusted certificates for path validation is expected to occur
      through an out-of-band transfer.
      Once the certificate has been found acceptable (either by path
      validation or directly matching a fingerprint in this table),
      this table is consulted to determine the appropriate
      tmSecurityName to identify with the remote connection.  This
      is done by considering each active row from this table in
      prioritized order according to its snmpTlstmCertToTSNID value.
      Each row's snmpTlstmCertToTSNFingerprint value determines
      whether the row is a match for the incoming connection:
          1) If the row's snmpTlstmCertToTSNFingerprint value
             identifies the presented certificate, then consider the
             row as a successful match.
          2) If the row's snmpTlstmCertToTSNFingerprint value
             identifies a locally held copy of a trusted CA
             certificate and that CA certificate was used to
             validate the path to the presented certificate, then
             consider the row as a successful match.
      Once a matching row has been found, the
      snmpTlstmCertToTSNMapType value can be used to determine how
      the tmSecurityName to associate with the session should be
      determined.  See the snmpTlstmCertToTSNMapType column's
      DESCRIPTION for details on determining the tmSecurityName
      value.  If it is impossible to determine a tmSecurityName from
      the row's data combined with the data presented in the

Hardaker Standards Track [Page 41] RFC 6353 TLS Transport Model for SNMP July 2011

      certificate, then additional rows MUST be searched looking for
      another potential match.  If a resulting tmSecurityName mapped
      from a given row is not compatible with the needed
      requirements of a tmSecurityName (e.g., VACM imposes a
      32-octet-maximum length and the certificate derived
      securityName could be longer), then it must be considered an
      invalid match and additional rows MUST be searched looking for
      another potential match.
      If no matching and valid row can be found, the connection MUST
      be closed and SNMP messages MUST NOT be accepted over it.
      Missing values of snmpTlstmCertToTSNID are acceptable and
      implementations should continue to the next highest numbered
      row.  It is recommended that administrators skip index values
      to leave room for the insertion of future rows (for example,
      use values of 10 and 20 when creating initial rows).
      Users are encouraged to make use of certificates with
      subjectAltName fields that can be used as tmSecurityNames so
      that a single root CA certificate can allow all child
      certificate's subjectAltName to map directly to a
      tmSecurityName via a 1:1 transformation.  However, this table
      is flexible to allow for situations where existing deployed
      certificate infrastructures do not provide adequate
      subjectAltName values for use as tmSecurityNames.
      Certificates may also be mapped to tmSecurityNames using the
      CommonName portion of the Subject field.  However, the usage
      of the CommonName field is deprecated and thus this usage is
      NOT RECOMMENDED.  Direct mapping from each individual
      certificate fingerprint to a tmSecurityName is also possible
      but requires one entry in the table per tmSecurityName and
      requires more management operations to completely configure a
      device."
  ::= { snmpTlstmCertificateMapping 3 }

snmpTlstmCertToTSNEntry OBJECT-TYPE

  SYNTAX      SnmpTlstmCertToTSNEntry
  MAX-ACCESS  not-accessible
  STATUS      current
  DESCRIPTION
      "A row in the snmpTlstmCertToTSNTable that specifies a mapping
      for an incoming (D)TLS certificate to a tmSecurityName to use
      for a connection."
  INDEX   { snmpTlstmCertToTSNID }
  ::= { snmpTlstmCertToTSNTable 1 }

Hardaker Standards Track [Page 42] RFC 6353 TLS Transport Model for SNMP July 2011

SnmpTlstmCertToTSNEntry ::= SEQUENCE {

  snmpTlstmCertToTSNID           Unsigned32,
  snmpTlstmCertToTSNFingerprint  SnmpTLSFingerprint,
  snmpTlstmCertToTSNMapType      AutonomousType,
  snmpTlstmCertToTSNData         OCTET STRING,
  snmpTlstmCertToTSNStorageType  StorageType,
  snmpTlstmCertToTSNRowStatus    RowStatus

}

snmpTlstmCertToTSNID OBJECT-TYPE

  SYNTAX      Unsigned32 (1..4294967295)
  MAX-ACCESS  not-accessible
  STATUS      current
  DESCRIPTION
      "A unique, prioritized index for the given entry.  Lower
      numbers indicate a higher priority."
  ::= { snmpTlstmCertToTSNEntry 1 }

snmpTlstmCertToTSNFingerprint OBJECT-TYPE

  SYNTAX      SnmpTLSFingerprint (SIZE(1..255))
  MAX-ACCESS  read-create
  STATUS      current
  DESCRIPTION
      "A cryptographic hash of an X.509 certificate.  The results of
      a successful matching fingerprint to either the trusted CA in
      the certificate validation path or to the certificate itself
      is dictated by the snmpTlstmCertToTSNMapType column."
  ::= { snmpTlstmCertToTSNEntry 2 }

snmpTlstmCertToTSNMapType OBJECT-TYPE

  SYNTAX      AutonomousType
  MAX-ACCESS  read-create
  STATUS      current
  DESCRIPTION
      "Specifies the mapping type for deriving a tmSecurityName from
      a certificate.  Details for mapping of a particular type SHALL
      be specified in the DESCRIPTION clause of the OBJECT-IDENTITY
      that describes the mapping.  If a mapping succeeds it will
      return a tmSecurityName for use by the TLSTM model and
      processing stops.
      If the resulting mapped value is not compatible with the
      needed requirements of a tmSecurityName (e.g., VACM imposes a
      32-octet-maximum length and the certificate derived
      securityName could be longer), then future rows MUST be
      searched for additional snmpTlstmCertToTSNFingerprint matches
      to look for a mapping that succeeds.

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      Suitable values for assigning to this object that are defined
      within the SNMP-TLS-TM-MIB can be found in the
      snmpTlstmCertToTSNMIdentities portion of the MIB tree."
  DEFVAL { snmpTlstmCertSpecified }
  ::= { snmpTlstmCertToTSNEntry 3 }

snmpTlstmCertToTSNData OBJECT-TYPE

  SYNTAX      OCTET STRING (SIZE(0..1024))
  MAX-ACCESS  read-create
  STATUS      current
  DESCRIPTION
      "Auxiliary data used as optional configuration information for
      a given mapping specified by the snmpTlstmCertToTSNMapType
      column.  Only some mapping systems will make use of this
      column.  The value in this column MUST be ignored for any
      mapping type that does not require data present in this
      column."
  DEFVAL { "" }
  ::= { snmpTlstmCertToTSNEntry 4 }

snmpTlstmCertToTSNStorageType OBJECT-TYPE

  SYNTAX       StorageType
  MAX-ACCESS   read-create
  STATUS       current
  DESCRIPTION
      "The storage type for this conceptual row.  Conceptual rows
      having the value 'permanent' need not allow write-access to
      any columnar objects in the row."
  DEFVAL      { nonVolatile }
  ::= { snmpTlstmCertToTSNEntry 5 }

snmpTlstmCertToTSNRowStatus OBJECT-TYPE

  SYNTAX      RowStatus
  MAX-ACCESS  read-create
  STATUS      current
  DESCRIPTION
      "The status of this conceptual row.  This object may be used
      to create or remove rows from this table.
      To create a row in this table, an administrator must set this
      object to either createAndGo(4) or createAndWait(5).
      Until instances of all corresponding columns are appropriately
      configured, the value of the corresponding instance of the
      snmpTlstmParamsRowStatus column is notReady(3).
      In particular, a newly created row cannot be made active until
      the corresponding snmpTlstmCertToTSNFingerprint,

Hardaker Standards Track [Page 44] RFC 6353 TLS Transport Model for SNMP July 2011

      snmpTlstmCertToTSNMapType, and snmpTlstmCertToTSNData columns
      have been set.
      The following objects may not be modified while the
      value of this object is active(1):
          - snmpTlstmCertToTSNFingerprint
          - snmpTlstmCertToTSNMapType
          - snmpTlstmCertToTSNData
      An attempt to set these objects while the value of
      snmpTlstmParamsRowStatus is active(1) will result in
      an inconsistentValue error."
  ::= { snmpTlstmCertToTSNEntry 6 }

– Maps tmSecurityNames to certificates for use by the SNMP-TARGET-MIB

snmpTlstmParamsCount OBJECT-TYPE

  SYNTAX      Gauge32
  MAX-ACCESS  read-only
  STATUS      current
  DESCRIPTION
      "A count of the number of entries in the snmpTlstmParamsTable."
  ::= { snmpTlstmCertificateMapping 4 }

snmpTlstmParamsTableLastChanged OBJECT-TYPE

  SYNTAX      TimeStamp
  MAX-ACCESS  read-only
  STATUS      current
  DESCRIPTION
      "The value of sysUpTime.0 when the snmpTlstmParamsTable
      was last modified through any means, or 0 if it has not been
      modified since the command responder was started."
  ::= { snmpTlstmCertificateMapping 5 }

snmpTlstmParamsTable OBJECT-TYPE

  SYNTAX      SEQUENCE OF SnmpTlstmParamsEntry
  MAX-ACCESS  not-accessible
  STATUS      current
  DESCRIPTION
      "This table is used by a (D)TLS client when a (D)TLS
      connection is being set up using an entry in the
      SNMP-TARGET-MIB.  It extends the SNMP-TARGET-MIB's
      snmpTargetParamsTable with a fingerprint of a certificate to
      use when establishing such a (D)TLS connection."
  ::= { snmpTlstmCertificateMapping 6 }

snmpTlstmParamsEntry OBJECT-TYPE

  SYNTAX      SnmpTlstmParamsEntry
  MAX-ACCESS  not-accessible

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  STATUS      current
  DESCRIPTION
      "A conceptual row containing a fingerprint hash of a locally
      held certificate for a given snmpTargetParamsEntry.  The
      values in this row should be ignored if the connection that
      needs to be established, as indicated by the SNMP-TARGET-MIB
      infrastructure, is not a certificate and (D)TLS based
      connection.  The connection SHOULD NOT be established if the
      certificate fingerprint stored in this entry does not point to
      a valid locally held certificate or if it points to an
      unusable certificate (such as might happen when the
      certificate's expiration date has been reached)."
  INDEX    { IMPLIED snmpTargetParamsName }
  ::= { snmpTlstmParamsTable 1 }

SnmpTlstmParamsEntry ::= SEQUENCE {

  snmpTlstmParamsClientFingerprint SnmpTLSFingerprint,
  snmpTlstmParamsStorageType       StorageType,
  snmpTlstmParamsRowStatus         RowStatus

}

snmpTlstmParamsClientFingerprint OBJECT-TYPE

  SYNTAX      SnmpTLSFingerprint
  MAX-ACCESS  read-create
  STATUS      current
  DESCRIPTION
      "This object stores the hash of the public portion of a
      locally held X.509 certificate.  The X.509 certificate, its
      public key, and the corresponding private key will be used
      when initiating a (D)TLS connection as a (D)TLS client."
  ::= { snmpTlstmParamsEntry 1 }

snmpTlstmParamsStorageType OBJECT-TYPE

  SYNTAX       StorageType
  MAX-ACCESS   read-create
  STATUS       current
  DESCRIPTION
      "The storage type for this conceptual row.  Conceptual rows
      having the value 'permanent' need not allow write-access to
      any columnar objects in the row."
  DEFVAL      { nonVolatile }
  ::= { snmpTlstmParamsEntry 2 }

snmpTlstmParamsRowStatus OBJECT-TYPE

  SYNTAX      RowStatus
  MAX-ACCESS  read-create
  STATUS      current
  DESCRIPTION

Hardaker Standards Track [Page 46] RFC 6353 TLS Transport Model for SNMP July 2011

      "The status of this conceptual row.  This object may be used
      to create or remove rows from this table.
      To create a row in this table, an administrator must set this
      object to either createAndGo(4) or createAndWait(5).
      Until instances of all corresponding columns are appropriately
      configured, the value of the corresponding instance of the
      snmpTlstmParamsRowStatus column is notReady(3).
      In particular, a newly created row cannot be made active until
      the corresponding snmpTlstmParamsClientFingerprint column has
      been set.
      The snmpTlstmParamsClientFingerprint object may not be modified
      while the value of this object is active(1).
      An attempt to set these objects while the value of
      snmpTlstmParamsRowStatus is active(1) will result in
      an inconsistentValue error."
  ::= { snmpTlstmParamsEntry 3 }

snmpTlstmAddrCount OBJECT-TYPE

  SYNTAX      Gauge32
  MAX-ACCESS  read-only
  STATUS      current
  DESCRIPTION
      "A count of the number of entries in the snmpTlstmAddrTable."
  ::= { snmpTlstmCertificateMapping 7 }

snmpTlstmAddrTableLastChanged OBJECT-TYPE

  SYNTAX      TimeStamp
  MAX-ACCESS  read-only
  STATUS      current
  DESCRIPTION
      "The value of sysUpTime.0 when the snmpTlstmAddrTable
      was last modified through any means, or 0 if it has not been
      modified since the command responder was started."
  ::= { snmpTlstmCertificateMapping 8 }

snmpTlstmAddrTable OBJECT-TYPE

  SYNTAX      SEQUENCE OF SnmpTlstmAddrEntry
  MAX-ACCESS  not-accessible
  STATUS      current
  DESCRIPTION
      "This table is used by a (D)TLS client when a (D)TLS
      connection is being set up using an entry in the
      SNMP-TARGET-MIB.  It extends the SNMP-TARGET-MIB's

Hardaker Standards Track [Page 47] RFC 6353 TLS Transport Model for SNMP July 2011

      snmpTargetAddrTable so that the client can verify that the
      correct server has been reached.  This verification can use
      either a certificate fingerprint, or an identity
      authenticated via certification path validation.
      If there is an active row in this table corresponding to the
      entry in the SNMP-TARGET-MIB that was used to establish the
      connection, and the row's snmpTlstmAddrServerFingerprint
      column has non-empty value, then the server's presented
      certificate is compared with the
      snmpTlstmAddrServerFingerprint value (and the
      snmpTlstmAddrServerIdentity column is ignored).  If the
      fingerprint matches, the verification has succeeded.  If the
      fingerprint does not match, then the connection MUST be
      closed.
      If the server's presented certificate has passed
      certification path validation [RFC5280] to a configured
      trust anchor, and an active row exists with a zero-length
      snmpTlstmAddrServerFingerprint value, then the
      snmpTlstmAddrServerIdentity column contains the expected
      host name.  This expected host name is then compared against
      the server's certificate as follows:
  1. Implementations MUST support matching the expected host

name against a dNSName in the subjectAltName extension

        field and MAY support checking the name against the
        CommonName portion of the subject distinguished name.
  1. The '*' (ASCII 0x2a) wildcard character is allowed in the

dNSName of the subjectAltName extension (and in common

        name, if used to store the host name), but only as the
        left-most (least significant) DNS label in that value.
        This wildcard matches any left-most DNS label in the
        server name.  That is, the subject *.example.com matches
        the server names a.example.com and b.example.com, but does
        not match example.com or a.b.example.com.  Implementations
        MUST support wildcards in certificates as specified above,
        but MAY provide a configuration option to disable them.
  1. If the locally configured name is an internationalized

domain name, conforming implementations MUST convert it to

        the ASCII Compatible Encoding (ACE) format for performing
        comparisons, as specified in Section 7 of [RFC5280].
      If the expected host name fails these conditions then the
      connection MUST be closed.

Hardaker Standards Track [Page 48] RFC 6353 TLS Transport Model for SNMP July 2011

      If there is no row in this table corresponding to the entry
      in the SNMP-TARGET-MIB and the server can be authorized by
      another, implementation-dependent means, then the connection
      MAY still proceed."
  ::= { snmpTlstmCertificateMapping 9 }

snmpTlstmAddrEntry OBJECT-TYPE

  SYNTAX      SnmpTlstmAddrEntry
  MAX-ACCESS  not-accessible
  STATUS      current
  DESCRIPTION
      "A conceptual row containing a copy of a certificate's
      fingerprint for a given snmpTargetAddrEntry.  The values in
      this row should be ignored if the connection that needs to be
      established, as indicated by the SNMP-TARGET-MIB
      infrastructure, is not a (D)TLS based connection.  If an
      snmpTlstmAddrEntry exists for a given snmpTargetAddrEntry, then
      the presented server certificate MUST match or the connection
      MUST NOT be established.  If a row in this table does not
      exist to match an snmpTargetAddrEntry row, then the connection
      SHOULD still proceed if some other certificate validation path
      algorithm (e.g., RFC 5280) can be used."
  INDEX    { IMPLIED snmpTargetAddrName }
  ::= { snmpTlstmAddrTable 1 }

SnmpTlstmAddrEntry ::= SEQUENCE {

  snmpTlstmAddrServerFingerprint    SnmpTLSFingerprint,
  snmpTlstmAddrServerIdentity       SnmpAdminString,
  snmpTlstmAddrStorageType          StorageType,
  snmpTlstmAddrRowStatus            RowStatus

}

snmpTlstmAddrServerFingerprint OBJECT-TYPE

  SYNTAX      SnmpTLSFingerprint
  MAX-ACCESS  read-create
  STATUS      current
  DESCRIPTION
      "A cryptographic hash of a public X.509 certificate.  This
      object should store the hash of the public X.509 certificate
      that the remote server should present during the (D)TLS
      connection setup.  The fingerprint of the presented
      certificate and this hash value MUST match exactly or the
      connection MUST NOT be established."
  DEFVAL { "" }
  ::= { snmpTlstmAddrEntry 1 }

Hardaker Standards Track [Page 49] RFC 6353 TLS Transport Model for SNMP July 2011

snmpTlstmAddrServerIdentity OBJECT-TYPE

  SYNTAX      SnmpAdminString
  MAX-ACCESS  read-create
  STATUS      current
  DESCRIPTION
      "The reference identity to check against the identity
      presented by the remote system."
  DEFVAL { "" }
  ::= { snmpTlstmAddrEntry 2 }

snmpTlstmAddrStorageType OBJECT-TYPE

  SYNTAX       StorageType
  MAX-ACCESS   read-create
  STATUS       current
  DESCRIPTION
      "The storage type for this conceptual row.  Conceptual rows
      having the value 'permanent' need not allow write-access to
      any columnar objects in the row."
  DEFVAL      { nonVolatile }
  ::= { snmpTlstmAddrEntry 3 }

snmpTlstmAddrRowStatus OBJECT-TYPE

  SYNTAX      RowStatus
  MAX-ACCESS  read-create
  STATUS      current
  DESCRIPTION
      "The status of this conceptual row.  This object may be used
      to create or remove rows from this table.
      To create a row in this table, an administrator must set this
      object to either createAndGo(4) or createAndWait(5).
      Until instances of all corresponding columns are
      appropriately configured, the value of the
      corresponding instance of the snmpTlstmAddrRowStatus
      column is notReady(3).
      In particular, a newly created row cannot be made active until
      the corresponding snmpTlstmAddrServerFingerprint column has been
      set.
      Rows MUST NOT be active if the snmpTlstmAddrServerFingerprint
      column is blank and the snmpTlstmAddrServerIdentity is set to
      '*' since this would insecurely accept any presented
      certificate.

Hardaker Standards Track [Page 50] RFC 6353 TLS Transport Model for SNMP July 2011

      The snmpTlstmAddrServerFingerprint object may not be modified
      while the value of this object is active(1).
      An attempt to set these objects while the value of
      snmpTlstmAddrRowStatus is active(1) will result in
      an inconsistentValue error."
  ::= { snmpTlstmAddrEntry 4 }

– snmpTlstmNotifications - Notifications Information –

snmpTlstmServerCertificateUnknown NOTIFICATION-TYPE

  OBJECTS { snmpTlstmSessionUnknownServerCertificate }
  STATUS  current
  DESCRIPTION
      "Notification that the server certificate presented by an SNMP
       over (D)TLS server was invalid because no configured
       fingerprint or CA was acceptable to validate it.  This may be
       because there was no entry in the snmpTlstmAddrTable or
       because no path could be found to known Certification
       Authority.
       To avoid notification loops, this notification MUST NOT be
       sent to servers that themselves have triggered the
       notification."
  ::= { snmpTlstmNotifications 1 }

snmpTlstmServerInvalidCertificate NOTIFICATION-TYPE

  OBJECTS { snmpTlstmAddrServerFingerprint,
            snmpTlstmSessionInvalidServerCertificates}
  STATUS  current
  DESCRIPTION
      "Notification that the server certificate presented by an SNMP
       over (D)TLS server could not be validated even if the
       fingerprint or expected validation path was known.  That is, a
       cryptographic validation error occurred during certificate
       validation processing.
       To avoid notification loops, this notification MUST NOT be
       sent to servers that themselves have triggered the
       notification."
  ::= { snmpTlstmNotifications 2 }

– snmpTlstmCompliances - Conformance Information –

Hardaker Standards Track [Page 51] RFC 6353 TLS Transport Model for SNMP July 2011

snmpTlstmCompliances OBJECT IDENTIFIER ::= { snmpTlstmConformance 1 }

snmpTlstmGroups OBJECT IDENTIFIER ::= { snmpTlstmConformance 2 }

– Compliance statements –

snmpTlstmCompliance MODULE-COMPLIANCE

  STATUS      current
  DESCRIPTION
      "The compliance statement for SNMP engines that support the
      SNMP-TLS-TM-MIB"
  MODULE
      MANDATORY-GROUPS { snmpTlstmStatsGroup,
                         snmpTlstmIncomingGroup,
                         snmpTlstmOutgoingGroup,
                         snmpTlstmNotificationGroup }
  ::= { snmpTlstmCompliances 1 }

– Units of conformance – snmpTlstmStatsGroup OBJECT-GROUP

  OBJECTS {
      snmpTlstmSessionOpens,
      snmpTlstmSessionClientCloses,
      snmpTlstmSessionOpenErrors,
      snmpTlstmSessionAccepts,
      snmpTlstmSessionServerCloses,
      snmpTlstmSessionNoSessions,
      snmpTlstmSessionInvalidClientCertificates,
      snmpTlstmSessionUnknownServerCertificate,
      snmpTlstmSessionInvalidServerCertificates,
      snmpTlstmSessionInvalidCaches
  }
  STATUS      current
  DESCRIPTION
      "A collection of objects for maintaining
      statistical information of an SNMP engine that
      implements the SNMP TLS Transport Model."
  ::= { snmpTlstmGroups 1 }

snmpTlstmIncomingGroup OBJECT-GROUP

  OBJECTS {
      snmpTlstmCertToTSNCount,
      snmpTlstmCertToTSNTableLastChanged,
      snmpTlstmCertToTSNFingerprint,

Hardaker Standards Track [Page 52] RFC 6353 TLS Transport Model for SNMP July 2011

      snmpTlstmCertToTSNMapType,
      snmpTlstmCertToTSNData,
      snmpTlstmCertToTSNStorageType,
      snmpTlstmCertToTSNRowStatus
  }
  STATUS      current
  DESCRIPTION
      "A collection of objects for maintaining
      incoming connection certificate mappings to
      tmSecurityNames of an SNMP engine that implements the
      SNMP TLS Transport Model."
  ::= { snmpTlstmGroups 2 }

snmpTlstmOutgoingGroup OBJECT-GROUP

  OBJECTS {
      snmpTlstmParamsCount,
      snmpTlstmParamsTableLastChanged,
      snmpTlstmParamsClientFingerprint,
      snmpTlstmParamsStorageType,
      snmpTlstmParamsRowStatus,
      snmpTlstmAddrCount,
      snmpTlstmAddrTableLastChanged,
      snmpTlstmAddrServerFingerprint,
      snmpTlstmAddrServerIdentity,
      snmpTlstmAddrStorageType,
      snmpTlstmAddrRowStatus
  }
  STATUS      current
  DESCRIPTION
      "A collection of objects for maintaining
      outgoing connection certificates to use when opening
      connections as a result of SNMP-TARGET-MIB settings."
  ::= { snmpTlstmGroups 3 }

snmpTlstmNotificationGroup NOTIFICATION-GROUP

  NOTIFICATIONS {
      snmpTlstmServerCertificateUnknown,
      snmpTlstmServerInvalidCertificate
  }
  STATUS current
  DESCRIPTION
      "Notifications"
  ::= { snmpTlstmGroups 4 }

END

Hardaker Standards Track [Page 53] RFC 6353 TLS Transport Model for SNMP July 2011

8. Operational Considerations

 This section discusses various operational aspects of deploying
 TLSTM.

8.1. Sessions

 A session is discussed throughout this document as meaning a security
 association between two TLSTM instances.  State information for the
 sessions are maintained in each TLSTM implementation and this
 information is created and destroyed as sessions are opened and
 closed.  A "broken" session (one side up and one side down) can
 result if one side of a session is brought down abruptly (i.e.,
 reboot, power outage, etc.).  Whenever possible, implementations
 SHOULD provide graceful session termination through the use of TLS
 disconnect messages.  Implementations SHOULD also have a system in
 place for detecting "broken" sessions through the use of heartbeats
 [HEARTBEAT] or other detection mechanisms.
 Implementations SHOULD limit the lifetime of established sessions
 depending on the algorithms used for generation of the master session
 secret, the privacy and integrity algorithms used to protect
 messages, the environment of the session, the amount of data
 transferred, and the sensitivity of the data.

8.2. Notification Receiver Credential Selection

 When an SNMP engine needs to establish an outgoing session for
 notifications, the snmpTargetParamsTable includes an entry for the
 snmpTargetParamsSecurityName of the target.  Servers that wish to
 support multiple principals at a particular port SHOULD make use of
 the Server Name Indication extension defined in Section 3.1 of
 [RFC4366].  Without the Server Name Indication the receiving SNMP
 engine (server) will not know which (D)TLS certificate to offer to
 the client so that the tmSecurityName identity-authentication will be
 successful.
 Another solution is to maintain a one-to-one mapping between
 certificates and incoming ports for notification receivers.  This can
 be handled at the notification originator by configuring the
 snmpTargetAddrTable (snmpTargetAddrTDomain and
 snmpTargetAddrTAddress) and requiring the receiving SNMP engine to
 monitor multiple incoming static ports based on which principals are
 capable of receiving notifications.
 Implementations MAY also choose to designate a single Notification
 Receiver Principal to receive all incoming notifications or select an

Hardaker Standards Track [Page 54] RFC 6353 TLS Transport Model for SNMP July 2011

 implementation specific method of selecting a server certificate to
 present to clients.

8.3. contextEngineID Discovery

 SNMPv3 requires that an application know the identifier
 (snmpEngineID) of the remote SNMP protocol engine in order to
 retrieve or manipulate objects maintained on the remote SNMP entity.
 [RFC5343] introduces a well-known localEngineID and a discovery
 mechanism that can be used to learn the snmpEngineID of a remote SNMP
 protocol engine.  Implementations are RECOMMENDED to support and use
 the contextEngineID discovery mechanism defined in [RFC5343].

8.4. Transport Considerations

 This document defines how SNMP messages can be transmitted over the
 TLS- and DTLS-based protocols.  Each of these protocols is
 additionally based on other transports (TCP and UDP).  These two base
 protocols also have operational considerations that must be taken
 into consideration when selecting a (D)TLS-based protocol to use such
 as its performance in degraded or limited networks.  It is beyond the
 scope of this document to summarize the characteristics of these
 transport mechanisms.  Please refer to the base protocol documents
 for details on messaging considerations with respect to MTU size,
 fragmentation, performance in lossy networks, etc.

9. Security Considerations

 This document describes a transport model that permits SNMP to
 utilize (D)TLS security services.  The security threats and how the
 (D)TLS transport model mitigates these threats are covered in detail
 throughout this document.  Security considerations for DTLS are
 covered in [RFC4347] and security considerations for TLS are
 described in Section 11 and Appendices D, E, and F of TLS 1.2
 [RFC5246].  When run over a connectionless transport such as UDP,
 DTLS is more vulnerable to denial-of-service attacks from spoofed IP
 addresses; see Section 4.2 for details how the cookie exchange is
 used to address this issue.

9.1. Certificates, Authentication, and Authorization

 Implementations are responsible for providing a security certificate
 installation and configuration mechanism.  Implementations SHOULD
 support certificate revocation lists.
 (D)TLS provides for authentication of the identity of both the (D)TLS
 server and the (D)TLS client.  Access to MIB objects for the

Hardaker Standards Track [Page 55] RFC 6353 TLS Transport Model for SNMP July 2011

 authenticated principal MUST be enforced by an access control
 subsystem (e.g., the VACM).
 Authentication of the command generator principal's identity is
 important for use with the SNMP access control subsystem to ensure
 that only authorized principals have access to potentially sensitive
 data.  The authenticated identity of the command generator
 principal's certificate is mapped to an SNMP model-independent
 securityName for use with SNMP access control.
 The (D)TLS handshake only provides assurance that the certificate of
 the authenticated identity has been signed by a configured accepted
 Certification Authority.  (D)TLS has no way to further authorize or
 reject access based on the authenticated identity.  An Access Control
 Model (such as the VACM) provides access control and authorization of
 a command generator's requests to a command responder and a
 notification receiver's authorization to receive Notifications from a
 notification originator.  However, to avoid man-in-the-middle
 attacks, both ends of the (D)TLS-based connection MUST check the
 certificate presented by the other side against what was expected.
 For example, command generators must check that the command responder
 presented and authenticated itself with an X.509 certificate that was
 expected.  Not doing so would allow an impostor, at a minimum, to
 present false data, receive sensitive information, and/or provide a
 false belief that configuration was actually received and acted upon.
 Authenticating and verifying the identity of the (D)TLS server and
 the (D)TLS client for all operations ensures the authenticity of the
 SNMP engine that provides MIB data.
 The instructions found in the DESCRIPTION clause of the
 snmpTlstmCertToTSNTable object must be followed exactly.  It is also
 important that the rows of the table be searched in prioritized order
 starting with the row containing the lowest numbered
 snmpTlstmCertToTSNID value.

9.2. (D)TLS Security Considerations

 This section discusses security considerations specific to the usage
 of (D)TLS.

9.2.1. TLS Version Requirements

 Implementations of TLS typically support multiple versions of the
 Transport Layer Security protocol as well as the older Secure Sockets
 Layer (SSL) protocol.  Because of known security vulnerabilities,
 TLSTM clients and servers MUST NOT request, offer, or use SSL 2.0.
 See Appendix E.2 of [RFC5246] for further details.

Hardaker Standards Track [Page 56] RFC 6353 TLS Transport Model for SNMP July 2011

9.2.2. Perfect Forward Secrecy

 The use of Perfect Forward Secrecy is RECOMMENDED and can be provided
 by (D)TLS with appropriately selected cipher_suites, as discussed in
 Appendix F of [RFC5246].

9.3. Use with SNMPv1/SNMPv2c Messages

 The SNMPv1 and SNMPv2c message processing described in [RFC3584] (BCP
 74) always selects the SNMPv1 or SNMPv2c Security Models,
 respectively.  Both of these and the User-based Security Model
 typically used with SNMPv3 derive the securityName and securityLevel
 from the SNMP message received, even when the message was received
 over a secure transport.  Access control decisions are therefore made
 based on the contents of the SNMP message, rather than using the
 authenticated identity and securityLevel provided by the TLS
 Transport Model.  It is RECOMMENDED that only SNMPv3 messages using
 the Transport Security Model (TSM) or another secure-transport aware
 security model be sent over the TLSTM transport.
 Using a non-transport-aware Security Model with a secure Transport
 Model is NOT RECOMMENDED.  See [RFC5590], Section 7.1 for additional
 details on the coexistence of security-aware transports and non-
 transport-aware security models.

9.4. MIB Module Security

 There are a number of management objects defined in this MIB module
 with a MAX-ACCESS clause of read-write and/or read-create.  Such
 objects may be considered sensitive or vulnerable in some network
 environments.  The support for SET operations in a non-secure
 environment without proper protection can have a negative effect on
 network operations.  These are the tables and objects and their
 sensitivity/vulnerability:
 o  The snmpTlstmParamsTable can be used to change the outgoing X.509
    certificate used to establish a (D)TLS connection.  Modifications
    to objects in this table need to be adequately authenticated since
    modifying the values in this table will have profound impacts to
    the security of outbound connections from the device.  Since
    knowledge of authorization rules and certificate usage mechanisms
    may be considered sensitive, protection from disclosure of the
    SNMP traffic via encryption is also highly recommended.
 o  The snmpTlstmAddrTable can be used to change the expectations of
    the certificates presented by a remote (D)TLS server.
    Modifications to objects in this table need to be adequately
    authenticated since modifying the values in this table will have

Hardaker Standards Track [Page 57] RFC 6353 TLS Transport Model for SNMP July 2011

    profound impacts to the security of outbound connections from the
    device.  Since knowledge of authorization rules and certificate
    usage mechanisms may be considered sensitive, protection from
    disclosure of the SNMP traffic via encryption is also highly
    recommended.
 o  The snmpTlstmCertToTSNTable is used to specify the mapping of
    incoming X.509 certificates to tmSecurityNames, which eventually
    get mapped to an SNMPv3 securityName.  Modifications to objects in
    this table need to be adequately authenticated since modifying the
    values in this table will have profound impacts to the security of
    incoming connections to the device.  Since knowledge of
    authorization rules and certificate usage mechanisms may be
    considered sensitive, protection from disclosure of the SNMP
    traffic via encryption is also highly recommended.  When this
    table contains a significant number of rows it may affect the
    system performance when accepting new (D)TLS connections.
 Some of the readable objects in this MIB module (i.e., objects with a
 MAX-ACCESS other than not-accessible) may be considered sensitive or
 vulnerable in some network environments.  It is thus important to
 control even GET and/or NOTIFY access to these objects and possibly
 to even encrypt the values of these objects when sending them over
 the network via SNMP.  These are the tables and objects and their
 sensitivity/vulnerability:
 o  This MIB contains a collection of counters that monitor the (D)TLS
    connections being established with a device.  Since knowledge of
    connection and certificate usage mechanisms may be considered
    sensitive, protection from disclosure of the SNMP traffic via
    encryption is highly recommended.
 SNMP versions prior to SNMPv3 did not include adequate security.
 Even if the network itself is secure (for example, by using IPsec),
 even then, there is no control as to who on the secure network is
 allowed to access and GET/SET (read/change/create/delete) the objects
 in this MIB module.
 It is RECOMMENDED that implementers consider the security features as
 provided by the SNMPv3 framework (see [RFC3410], Section 8),
 including full support for the SNMPv3 cryptographic mechanisms (for
 authentication and privacy).
 Further, deployment of SNMP versions prior to SNMPv3 is NOT
 RECOMMENDED.  Instead, it is RECOMMENDED to deploy SNMPv3 and to
 enable cryptographic security.  It is then a customer/operator
 responsibility to ensure that the SNMP entity giving access to an
 instance of this MIB module is properly configured to give access to

Hardaker Standards Track [Page 58] RFC 6353 TLS Transport Model for SNMP July 2011

 the objects only to those principals (users) that have legitimate
 rights to indeed GET or SET (change/create/delete) them.

10. IANA Considerations

 IANA has assigned:
 1.  Two TCP/UDP port numbers from the "Registered Ports" range of the
     Port Numbers registry, with the following keywords:
   Keyword         Decimal      Description       References
   -------         -------      -----------       ----------
   snmptls         10161/tcp    SNMP-TLS          [RFC6353]
   snmpdtls        10161/udp    SNMP-DTLS         [RFC6353]
   snmptls-trap    10162/tcp    SNMP-Trap-TLS     [RFC6353]
   snmpdtls-trap   10162/udp    SNMP-Trap-DTLS    [RFC6353]
 These are the default ports for receipt of SNMP command messages
 (snmptls and snmpdtls) and SNMP notification messages (snmptls-trap
 and snmpdtls-trap) over a TLS Transport Model as defined in this
 document.
 2.  An SMI number (8) under snmpDomains for the snmpTLSTCPDomain
     object identifier
 3.  An SMI number (9) under snmpDomains for the snmpDTLSUDPDomain
     object identifier
 4.  An SMI number (198) under mib-2, for the MIB module in this
     document
 5.  "tls" as the corresponding prefix for the snmpTLSTCPDomain in the
     SNMP Transport Domains registry
 6.  "dtls" as the corresponding prefix for the snmpDTLSUDPDomain in
     the SNMP Transport Domains registry

11. Acknowledgements

 This document closely follows and copies the Secure Shell Transport
 Model for SNMP documented by David Harrington and Joseph Salowey in
 [RFC5592].
 This document was reviewed by the following people who helped provide
 useful comments (in alphabetical order): Andy Donati, Pasi Eronen,
 David Harrington, Jeffrey Hutzelman, Alan Luchuk, Michael Peck, Tom
 Petch, Randy Presuhn, Ray Purvis, Peter Saint-Andre, Joseph Salowey,
 Juergen Schoenwaelder, Dave Shield, and Robert Story.

Hardaker Standards Track [Page 59] RFC 6353 TLS Transport Model for SNMP July 2011

 This work was supported in part by the United States Department of
 Defense.  Large portions of this document are based on work by
 General Dynamics C4 Systems and the following individuals: Brian
 Baril, Kim Bryant, Dana Deluca, Dan Hanson, Tim Huemiller, John
 Holzhauer, Colin Hoogeboom, Dave Kornbau, Chris Knaian, Dan Knaul,
 Charles Limoges, Steve Moccaldi, Gerardo Orlando, and Brandon Yip.

12. References

12.1. Normative References

 [RFC1123]    Braden, R., "Requirements for Internet Hosts -
              Application and Support", STD 3, RFC 1123, October 1989.
 [RFC2119]    Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC2578]    McCloghrie, K., Ed., Perkins, D., Ed., and J.
              Schoenwaelder, Ed., "Structure of Management Information
              Version 2 (SMIv2)", STD 58, RFC 2578, April 1999.
 [RFC2579]    McCloghrie, K., Ed., Perkins, D., Ed., and J.
              Schoenwaelder, Ed., "Textual Conventions for SMIv2",
              STD 58, RFC 2579, April 1999.
 [RFC2580]    McCloghrie, K., Perkins, D., and J. Schoenwaelder,
              "Conformance Statements for SMIv2", STD 58, RFC 2580,
              April 1999.
 [RFC3411]    Harrington, D., Presuhn, R., and B. Wijnen, "An
              Architecture for Describing Simple Network Management
              Protocol (SNMP) Management Frameworks", STD 62,
              RFC 3411, December 2002.
 [RFC3413]    Levi, D., Meyer, P., and B. Stewart, "Simple Network
              Management Protocol (SNMP) Applications", STD 62,
              RFC 3413, December 2002.
 [RFC3414]    Blumenthal, U. and B. Wijnen, "User-based Security Model
              (USM) for version 3 of the Simple Network Management
              Protocol (SNMPv3)", STD 62, RFC 3414, December 2002.
 [RFC3415]    Wijnen, B., Presuhn, R., and K. McCloghrie, "View-based
              Access Control Model (VACM) for the Simple Network
              Management Protocol (SNMP)", STD 62, RFC 3415,
              December 2002.

Hardaker Standards Track [Page 60] RFC 6353 TLS Transport Model for SNMP July 2011

 [RFC3418]    Presuhn, R., "Management Information Base (MIB) for the
              Simple Network Management Protocol (SNMP)", STD 62,
              RFC 3418, December 2002.
 [RFC3584]    Frye, R., Levi, D., Routhier, S., and B. Wijnen,
              "Coexistence between Version 1, Version 2, and Version 3
              of the Internet-standard Network Management Framework",
              BCP 74, RFC 3584, August 2003.
 [RFC4347]    Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security", RFC 4347, April 2006.
 [RFC4366]    Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen,
              J., and T. Wright, "Transport Layer Security (TLS)
              Extensions", RFC 4366, April 2006.
 [RFC5246]    Dierks, T. and E. Rescorla, "The Transport Layer
              Security (TLS) Protocol Version 1.2", RFC 5246,
              August 2008.
 [RFC5280]    Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation
              List (CRL) Profile", RFC 5280, May 2008.
 [RFC5590]    Harrington, D. and J. Schoenwaelder, "Transport
              Subsystem for the Simple Network Management Protocol
              (SNMP)", RFC 5590, June 2009.
 [RFC5591]    Harrington, D. and W. Hardaker, "Transport Security
              Model for the Simple Network Management Protocol
              (SNMP)", RFC 5591, June 2009.
 [RFC5952]    Kawamura, S. and M. Kawashima, "A Recommendation for
              IPv6 Address Text Representation", RFC 5952,
              August 2010.

12.2. Informative References

 [HEARTBEAT]  Seggelmann, R., Tuexen, M., and M. Williams, "Transport
              Layer Security (TLS) and Datagram Transport Layer
              Security (DTLS) Heartbeat Extension", Work in Progress,
              July 2011.
 [RFC3410]    Case, J., Mundy, R., Partain, D., and B. Stewart,
              "Introduction and Applicability Statements for Internet-
              Standard Management Framework", RFC 3410, December 2002.

Hardaker Standards Track [Page 61] RFC 6353 TLS Transport Model for SNMP July 2011

 [RFC5343]    Schoenwaelder, J., "Simple Network Management Protocol
              (SNMP) Context EngineID Discovery", RFC 5343,
              September 2008.
 [RFC5592]    Harrington, D., Salowey, J., and W. Hardaker, "Secure
              Shell Transport Model for the Simple Network Management
              Protocol (SNMP)", RFC 5592, June 2009.
 [RFC5890]    Klensin, J., "Internationalized Domain Names for
              Applications (IDNA): Definitions and Document
              Framework", RFC 5890, August 2010.
 [RFC5953]    Hardaker, W., "Transport Layer Security (TLS) Transport
              Model for the Simple Network Management Protocol
              (SNMP)", RFC 5953, August 2010.

Hardaker Standards Track [Page 62] RFC 6353 TLS Transport Model for SNMP July 2011

Appendix A. Target and Notification Configuration Example

 The following sections describe example configuration for the SNMP-
 TLS-TM-MIB, the SNMP-TARGET-MIB, the NOTIFICATION-MIB, and the SNMP-
 VIEW-BASED-ACM-MIB.

A.1. Configuring a Notification Originator

 The following row adds the "Joe Cool" user to the "administrators"
 group:
     vacmSecurityModel              = 4 (TSM)
     vacmSecurityName               = "Joe Cool"
     vacmGroupName                  = "administrators"
     vacmSecurityToGroupStorageType = 3 (nonVolatile)
     vacmSecurityToGroupStatus      = 4 (createAndGo)
 The following row configures the snmpTlstmAddrTable to use
 certificate path validation and to require the remote notification
 receiver to present a certificate for the "server.example.org"
 identity.
     snmpTargetAddrName             =  "toNRAddr"
     snmpTlstmAddrServerFingerprint =  ""
     snmpTlstmAddrServerIdentity    =  "server.example.org"
     snmpTlstmAddrStorageType       =  3         (nonVolatile)
     snmpTlstmAddrRowStatus         =  4         (createAndGo)
 The following row configures the snmpTargetAddrTable to send
 notifications using TLS/TCP to the snmptls-trap port at 192.0.2.1:
     snmpTargetAddrName              = "toNRAddr"
     snmpTargetAddrTDomain           = snmpTLSTCPDomain
     snmpTargetAddrTAddress          = "192.0.2.1:10162"
     snmpTargetAddrTimeout           = 1500
     snmpTargetAddrRetryCount        = 3
     snmpTargetAddrTagList           = "toNRTag"
     snmpTargetAddrParams            = "toNR"     (MUST match below)
     snmpTargetAddrStorageType       = 3          (nonVolatile)
     snmpTargetAddrRowStatus         = 4          (createAndGo)

Hardaker Standards Track [Page 63] RFC 6353 TLS Transport Model for SNMP July 2011

 The following row configures the snmpTargetParamsTable to send the
 notifications to "Joe Cool", using authPriv SNMPv3 notifications
 through the TransportSecurityModel [RFC5591]:
     snmpTargetParamsName            = "toNR"     (must match above)
     snmpTargetParamsMPModel         = 3 (SNMPv3)
     snmpTargetParamsSecurityModel   = 4 (TransportSecurityModel)
     snmpTargetParamsSecurityName    = "Joe Cool"
     snmpTargetParamsSecurityLevel   = 3          (authPriv)
     snmpTargetParamsStorageType     = 3          (nonVolatile)
     snmpTargetParamsRowStatus       = 4          (createAndGo)

A.2. Configuring TLSTM to Utilize a Simple Derivation of tmSecurityName

 The following row configures the snmpTlstmCertToTSNTable to map a
 validated client certificate, referenced by the client's public X.509
 hash fingerprint, to a tmSecurityName using the subjectAltName
 component of the certificate.
     snmpTlstmCertToTSNID          = 1
                                     (chosen by ordering preference)
     snmpTlstmCertToTSNFingerprint = HASH (appropriate fingerprint)
     snmpTlstmCertToTSNMapType     = snmpTlstmCertSANAny
     snmpTlstmCertToTSNData        = ""  (not used)
     snmpTlstmCertToTSNStorageType = 3   (nonVolatile)
     snmpTlstmCertToTSNRowStatus   = 4   (createAndGo)
 This type of configuration should only be used when the naming
 conventions of the (possibly multiple) Certification Authorities are
 well understood, so two different principals cannot inadvertently be
 identified by the same derived tmSecurityName.

A.3. Configuring TLSTM to Utilize Table-Driven Certificate Mapping

 The following row configures the snmpTlstmCertToTSNTable to map a
 validated client certificate, referenced by the client's public X.509
 hash fingerprint, to the directly specified tmSecurityName of "Joe
 Cool".
     snmpTlstmCertToTSNID           = 2
                                      (chosen by ordering preference)
     snmpTlstmCertToTSNFingerprint  = HASH (appropriate fingerprint)
     snmpTlstmCertToTSNMapType      = snmpTlstmCertSpecified
     snmpTlstmCertToTSNSecurityName = "Joe Cool"
     snmpTlstmCertToTSNStorageType  = 3  (nonVolatile)
     snmpTlstmCertToTSNRowStatus    = 4  (createAndGo)

Hardaker Standards Track [Page 64] RFC 6353 TLS Transport Model for SNMP July 2011

Author's Address

 Wes Hardaker
 SPARTA, Inc.
 P.O. Box 382
 Davis, CA  95617
 USA
 Phone: +1 530 792 1913
 EMail: ietf@hardakers.net

Hardaker Standards Track [Page 65]

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